Short Duration Contracts - Claims development - Mortgage (Details) $ in Thousands	Dec. 31, 2021 USD ($) claims	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Claims Development [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	$ 11,886,330
Mortgage
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	2,268,206
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	1,593,806
All outstanding liabilities before 2012, net of reinsurance	14,288
Mortgage | 2012
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	456,362	$ 456,331	$ 456,286	$ 458,065	$ 459,467	$ 467,296	$ 469,238	$ 475,317	$ 480,592	$ 520,835
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	453,986	453,587	452,348	448,151	441,577	426,024	395,695	327,605	186,605	$ (106,065)
Total of IBNR liabilities plus expected development on reported claims	$ 1
Cumulative number of paid claims | claims	15,080
Mortgage | 2013
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 391,324	391,062	390,987	393,149	395,693	405,809	411,793	419,668	469,311
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	387,879	387,894	386,853	382,200	373,909	353,189	308,956	203,957	$ 41,447
Total of IBNR liabilities plus expected development on reported claims	$ 1
Cumulative number of paid claims | claims	9,468
Mortgage | 2014
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 262,829	262,682	261,091	265,992	266,027	279,434	297,151	316,095
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	256,875	256,285	254,175	247,038	233,879	201,925	129,159	$ 20,099
Total of IBNR liabilities plus expected development on reported claims	$ 4
Cumulative number of paid claims | claims	6,299
Mortgage | 2015
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 190,560	190,913	189,235	194,677	198,001	197,238	222,790
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	184,025	183,472	180,321	171,337	151,222	92,431	$ 16,159
Total of IBNR liabilities plus expected development on reported claims	$ 1
Cumulative number of paid claims | claims	4,554
Mortgage | 2016
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 141,657	142,392	140,608	148,715	170,532	183,556
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	131,717	131,161	127,286	113,357	72,201	$ 11,462
Total of IBNR liabilities plus expected development on reported claims	$ 1
Cumulative number of paid claims | claims	3,424
Mortgage | 2017
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 109,242	108,181	107,255	132,220	179,376
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	89,756	87,317	78,650	48,112	$ 8,622
Total of IBNR liabilities plus expected development on reported claims	$ 1
Cumulative number of paid claims | claims	2,474
Mortgage | 2018
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 87,962	89,120	96,357	132,318
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	55,853	50,135	31,478	$ 3,966
Total of IBNR liabilities plus expected development on reported claims	$ 60
Cumulative number of paid claims | claims	1,635
Mortgage | 2019
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 110,362	119,253	108,424
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	29,102	20,105	$ 2,899
Total of IBNR liabilities plus expected development on reported claims	$ 181
Cumulative number of paid claims | claims	851
Mortgage | 2020
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 373,533	420,003
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	4,144	$ 1,040
Total of IBNR liabilities plus expected development on reported claims	$ 2,686
Cumulative number of paid claims | claims	189
Mortgage | 2021
Claims Development [Line Items]
Incurred losses and allocated loss adjustment expenses, net of reinsurance	$ 144,375
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance	469
Total of IBNR liabilities plus expected development on reported claims	$ 2,246
Cumulative number of paid claims | claims	11