Bank subsidiary (Details 7) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	$ 41,985	$ 37,906
Charge-offs	(2,178)	(12,830)
Recoveries	1,065	4,026
Provision	1,858	12,883
Valuation allowance, balance at the end of the period	42,730	41,985
Ending balance: individually evaluated for impairment	7,851	6,799
Ending balance: collectively evaluated for impairment	34,879	35,186
Financing Receivables:
Ending balance	3,855,835	3,790,856
Ending balance: individually evaluated for impairment	74,182	72,473
Ending balance: collectively evaluated for impairment	3,781,653	3,718,383
Residential 1-4 family
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	6,068	6,500
Charge-offs	(210)	(3,183)
Recoveries	192	1,328
Provision	(39)	1,423
Valuation allowance, balance at the end of the period	6,011	6,068
Ending balance: individually evaluated for impairment	454	384
Ending balance: collectively evaluated for impairment	5,557	5,684
Financing Receivables:
Ending balance	1,915,207	1,866,450
Ending balance: individually evaluated for impairment	25,320	25,279
Ending balance: collectively evaluated for impairment	1,889,887	1,841,171
Commercial real estate
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	2,965	1,688
Provision	3,691	1,277
Valuation allowance, balance at the end of the period	6,656	2,965
Ending balance: individually evaluated for impairment	3,169	535
Ending balance: collectively evaluated for impairment	3,487	2,430
Financing Receivables:
Ending balance	391,679	375,677
Ending balance: individually evaluated for impairment	10,662	6,751
Ending balance: collectively evaluated for impairment	381,017	368,926
Home equity line of credit
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	4,493	4,354
Charge-offs	(670)	(716)
Recoveries	194	108
Provision	540	747
Valuation allowance, balance at the end of the period	4,557	4,493
Ending balance: collectively evaluated for impairment	4,557	4,493
Financing Receivables:
Ending balance	648,904	630,175
Ending balance: individually evaluated for impairment	1,259	1,560
Ending balance: collectively evaluated for impairment	647,645	628,615
Residential land
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	4,275	3,795
Charge-offs	(227)	(2,808)
Recoveries	137	1,443
Provision	(1,442)	1,845
Valuation allowance, balance at the end of the period	2,743	4,275
Ending balance: individually evaluated for impairment	1,943	3,221
Ending balance: collectively evaluated for impairment	800	1,054
Financing Receivables:
Ending balance	23,894	25,815
Ending balance: individually evaluated for impairment	17,618	18,563
Ending balance: collectively evaluated for impairment	6,276	7,252
Commercial construction
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	2,023	1,888
Provision	(151)	135
Valuation allowance, balance at the end of the period	1,872	2,023
Ending balance: collectively evaluated for impairment	1,872	2,023
Financing Receivables:
Ending balance	40,698	43,988
Ending balance: collectively evaluated for impairment	40,698	43,988
Residential construction
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	9	4
Provision	3	5
Valuation allowance, balance at the end of the period	12	9
Ending balance: collectively evaluated for impairment	12	9
Financing Receivables:
Ending balance	8,275	6,171
Ending balance: collectively evaluated for impairment	8,275	6,171
Commercial loans
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	15,931	14,867
Charge-offs	(426)	(3,606)
Recoveries	392	649
Provision	(934)	4,021
Valuation allowance, balance at the end of the period	14,963	15,931
Ending balance: individually evaluated for impairment	2,285	2,659
Ending balance: collectively evaluated for impairment	12,678	13,272
Financing Receivables:
Ending balance	699,918	721,349
Ending balance: individually evaluated for impairment	19,302	20,298
Ending balance: collectively evaluated for impairment	680,616	701,051
Consumer loans
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	4,019	3,806
Charge-offs	(645)	(2,517)
Recoveries	150	498
Provision	131	2,232
Valuation allowance, balance at the end of the period	3,655	4,019
Ending balance: collectively evaluated for impairment	3,655	4,019
Financing Receivables:
Ending balance	127,260	121,231
Ending balance: individually evaluated for impairment	21	22
Ending balance: collectively evaluated for impairment	127,239	121,209
Unallocated
Allowance for loan losses:
Valuation allowance, balance at the beginning of the period	2,202	1,004
Provision	59	1,198
Valuation allowance, balance at the end of the period	2,261	2,202
Ending balance: collectively evaluated for impairment	$ 2,261	$ 2,202