RESERVE FOR LOSSES AND LOSS EXPENSES (DETAILS 6) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 7,426,671
Insurance [Member]
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	3,212,646
Insurance [Member] | Property and Other Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,455,975
All outstanding liabilities before 2007, net of reinsurance	5,376
Liabilities for claims and claim adjustment expenses, net of reinsurance	582,637
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	173,233
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	280,577	$ 124,166
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	398,150	345,785	$ 173,615
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	359,867	345,866	302,372	$ 128,519
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	372,567	364,966	341,818	278,331	$ 107,441
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	305,007	305,184	304,349	282,382	221,701	$ 88,982
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	111,349	111,543	111,450	107,257	96,449	87,621	$ 48,970
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	79,717	79,435	77,228	76,212	75,366	71,529	63,009	$ 34,370
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	228,945	228,989	229,498	227,438	224,874	197,852	186,147	164,425	$ 83,640
Insurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	146,563	146,807	146,717	146,404	139,931	137,481	134,379	126,050	105,253	$ 54,533
Insurance [Member] | Marine Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	534,472
All outstanding liabilities before 2007, net of reinsurance	6,114
Liabilities for claims and claim adjustment expenses, net of reinsurance	253,308
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,459
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	54,575	21,584
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	26,111	14,877	6,359
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	61,737	53,633	43,193	18,309
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	49,891	49,100	44,463	38,301	10,669
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	60,181	59,481	57,677	54,618	44,004	26,431
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	45,634	44,730	43,962	41,158	32,327	27,822	17,387
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	49,845	49,588	47,082	46,490	44,535	40,968	31,745	18,938
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	83,772	83,692	83,546	83,465	79,737	78,641	70,590	54,266	22,745
Insurance [Member] | Marine Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	90,267	90,115	86,792	85,211	85,219	82,021	76,551	57,907	35,176	14,828
Insurance [Member] | Aviation Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	101,322
All outstanding liabilities before 2007, net of reinsurance	2,410
Liabilities for claims and claim adjustment expenses, net of reinsurance	54,550
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	10,396
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	16,137	8,077
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	11,672	8,011	3,985
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	11,427	9,731	7,317	4,398
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,793	5,927	4,133	2,848	951
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,796	5,547	5,015	4,499	2,813	638
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,788	7,345	7,230	6,567	5,995	3,819	745
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	13,617	14,120	14,183	13,819	12,697	6,957	3,516	2,022
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,514	5,258	4,651	4,475	4,205	3,655	3,074	2,057	488
Insurance [Member] | Aviation Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,182	12,148	12,126	12,129	11,781	11,100	10,498	9,219	6,692	2,400
Insurance [Member] | Credit and Political Risk Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	613,658
All outstanding liabilities before 2007, net of reinsurance	20
Liabilities for claims and claim adjustment expenses, net of reinsurance	51,637
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	0
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	23,309	0
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	61,108	39,951	1,924
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,216	3,726	2,235	745
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	36	0	0	0	0
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,636	27,636	27,636	27,636	37,205	32,788
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	102,152	101,946	101,784	106,766	90,729	85,418	50,000
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	345,555	345,507	345,508	341,564	346,209	346,248	344,648	92,841
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	44,410	44,410	44,410	45,379	45,379	45,638	45,625	69,217	0
Insurance [Member] | Credit and Political Risk Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,236	4,236	4,236	4,236	4,236	4,236	4,236	4,263	2,798	0
Insurance [Member] | Professional Lines Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,620,938
All outstanding liabilities before 2007, net of reinsurance	31,393
Liabilities for claims and claim adjustment expenses, net of reinsurance	1,717,559
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,707
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	68,050	20,745
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	132,966	73,828	25,351
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	182,468	136,542	75,901	18,305
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	240,671	194,031	106,822	44,804	8,895
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	250,219	177,629	117,097	78,605	36,396	8,470
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	119,939	109,403	96,431	78,663	57,282	30,353	8,179
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	174,032	136,271	117,174	105,510	76,121	49,396	24,559	4,251
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	267,314	249,050	214,542	189,952	167,923	125,594	68,355	22,565	5,154
Insurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	169,572	168,368	161,153	150,649	139,144	114,021	102,031	49,258	18,301	3,817
Insurance [Member] | Liability Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	512,474
All outstanding liabilities before 2007, net of reinsurance	39,713
Liabilities for claims and claim adjustment expenses, net of reinsurance	552,955
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,307
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	22,323	5,437
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	49,816	18,620	1,410
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	42,044	33,314	23,275	2,355
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	37,138	30,144	15,410	5,513	1,630
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	54,996	46,074	38,376	20,190	10,540	2,761
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	71,792	66,118	61,033	53,584	30,791	15,968	1,030
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	83,991	44,105	41,322	31,865	26,754	13,305	4,646	726
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	61,618	55,314	51,776	47,447	37,408	27,861	18,507	8,796	1,906
Insurance [Member] | Liability Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	82,449	80,150	76,411	69,335	60,080	52,660	40,853	22,206	5,968	436
Reinsurance [Member]
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	4,214,025
Reinsurance [Member] | Property and Other Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,699,618
All outstanding liabilities before 2007, net of reinsurance	4,498
Liabilities for claims and claim adjustment expenses, net of reinsurance	823,463
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	77,205
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	187,229	48,121
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	346,856	271,621	65,721
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	355,706	328,765	218,110	54,451
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	337,115	322,801	300,983	228,876	92,620
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	961,477	888,222	859,089	759,930	557,409	246,222
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	519,128	494,362	465,358	419,571	388,310	296,764	104,263
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	188,103	186,448	183,729	184,513	174,250	156,617	126,587	55,694
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	509,433	510,628	505,939	506,139	502,377	489,821	437,973	312,580	157,415
Reinsurance [Member] | Property and Other Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	217,366	215,894	217,756	219,809	215,294	211,499	203,754	189,166	159,438	58,955
Reinsurance [Member] | Credit and Surety Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	756,004
All outstanding liabilities before 2007, net of reinsurance	3,865
Liabilities for claims and claim adjustment expenses, net of reinsurance	356,668
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	41,768
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	79,523	32,757
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	83,536	59,406	35,261
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	95,282	88,904	74,740	32,113
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	104,802	101,328	95,544	82,707	48,576
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	79,807	77,734	73,282	66,120	50,959	22,198
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	58,579	57,263	56,304	54,849	54,023	44,156	25,558
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	83,185	83,338	83,281	80,635	76,863	74,948	73,878	31,892
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	82,026	81,790	81,152	79,414	77,425	75,801	61,530	63,686	20,345
Reinsurance [Member] | Credit and Surety Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	47,496	46,734	46,356	36,580	35,328	34,476	33,178	28,797	24,105	13,612
Reinsurance [Member] | Professional Lines Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	797,667
All outstanding liabilities before 2007, net of reinsurance	26,189
Liabilities for claims and claim adjustment expenses, net of reinsurance	1,154,464
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,755
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	13,503	3,134
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	48,714	13,049	2,019
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	64,809	30,403	12,020	1,059
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	85,753	53,440	29,527	10,346	776
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	102,813	84,672	57,119	30,216	11,812	1,510
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	123,711	107,096	76,635	52,066	31,198	12,000	1,740
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	137,842	127,697	108,140	83,537	62,988	32,286	8,588	914
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	132,194	123,672	108,226	91,554	70,329	49,053	21,620	6,411	373
Reinsurance [Member] | Professional Lines Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	86,573	82,406	73,941	70,636	60,188	54,438	34,567	21,286	4,133	56
Reinsurance [Member] | Motor Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	559,617
All outstanding liabilities before 2007, net of reinsurance	78,865
Liabilities for claims and claim adjustment expenses, net of reinsurance	811,156
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	59,989
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	89,516	56,940
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	88,652	70,547	42,546
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	72,085	62,830	50,230	33,173
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	80,182	74,063	64,918	50,904	28,703
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	80,593	74,955	68,802	58,841	45,270	23,397
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,017	23,957	19,972	17,068	13,939	9,299	5,138
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	24,535	20,167	17,973	12,037	8,761	7,346	6,343	2,533
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,452	13,975	13,366	10,788	8,438	6,984	5,827	5,612	2,741
Reinsurance [Member] | Motor Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	21,596	20,433	18,527	13,710	11,616	9,939	6,127	4,150	3,881	1,663
Reinsurance [Member] | Liability Reserve Class [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	710,523
All outstanding liabilities before 2007, net of reinsurance	28,494
Liabilities for claims and claim adjustment expenses, net of reinsurance	1,068,274
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	11,859
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,440	7,267
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	48,363	28,645	7,086
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	69,021	52,299	22,214	5,965
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	78,037	58,639	28,354	12,791	3,540
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	112,066	92,221	69,886	39,983	21,274	5,190
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	108,476	97,167	83,542	62,207	46,123	17,576	2,405
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2009 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	127,354	123,051	103,871	73,197	56,586	44,429	17,100	1,703
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	57,686	53,578	51,786	43,397	36,497	29,991	21,917	9,940	2,156
Reinsurance [Member] | Liability Reserve Class [Member] | Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 70,221	$ 66,791	$ 65,026	$ 59,966	$ 54,374	$ 42,081	$ 32,641	$ 22,833	$ 10,663	$ 2,556