Loans and Allowance for Loan Losses - Balance and activity in the allowance for loan losses by portfolio segment and recorded investment in loans by portfolio segment (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Allowance for loan losses:
Balance beginning of period			$ 107,137
Balance end of period	105,753	113,601	107,137
Ending allowance attributable to loans:
Individually evaluated for impairment		16,249
Collectively evaluated for impairment		97,352
Total ending allowance balance	105,753	113,601	107,137
Loans:
Individually evaluated for impairment		294,020
Collectively evaluated for impairment		3,833,546
Total loans	4,193,560	4,127,566	4,175,008
Loans Receivable
Allowance for loan losses:
Balance beginning of period	107,137	114,468
Charge-offs	(13,367)	(17,197)
Recoveries	983	1,330
Provision	11,000	15,000
Balance end of period	105,753	113,601
Ending allowance attributable to loans:
Individually evaluated for impairment	11,971	16,249	11,644
Collectively evaluated for impairment	93,782	97,352	95,493
Total ending allowance balance	105,753	113,601
Loans:
Individually evaluated for impairment	230,794	294,020	252,810
Collectively evaluated for impairment	3,962,766	3,833,546	3,922,198
Total loans	4,193,560	4,127,566	4,175,008
Loans Receivable | Commercial (secured by real estate)
Allowance for loan losses:
Balance beginning of period	27,847	31,644
Charge-offs	(5,454)	(3,928)
Recoveries	211	231
Provision	7,804	2,667
Balance end of period	30,408	30,614
Ending allowance attributable to loans:
Individually evaluated for impairment	5,089	7,654	6,106
Collectively evaluated for impairment	25,319	22,960	21,741
Total ending allowance balance	30,408	30,614
Loans:
Individually evaluated for impairment	86,978	117,999	104,409
Collectively evaluated for impairment	1,717,052	1,725,208	1,708,956
Total loans	1,804,030	1,843,207	1,813,365
Loans Receivable | Commercial & industrial
Allowance for loan losses:
Balance beginning of period	5,537	5,681
Charge-offs	(1,823)	(756)
Recoveries	322	87
Provision	1,590	460
Balance end of period	5,626	5,472
Ending allowance attributable to loans:
Individually evaluated for impairment	1,026	1,122	490
Collectively evaluated for impairment	4,600	4,350	5,047
Total ending allowance balance	5,626	5,472
Loans:
Individually evaluated for impairment	50,347	60,568	51,501
Collectively evaluated for impairment	403,417	378,928	406,745
Total loans	453,764	439,496	458,246
Loans Receivable | Commercial construction
Allowance for loan losses:
Balance beginning of period	8,389	6,097
Charge-offs	(45)	(364)
Recoveries	49	30
Provision	(285)	3,820
Balance end of period	8,108	9,583
Ending allowance attributable to loans:
Individually evaluated for impairment	2,093	1,920	2,239
Collectively evaluated for impairment	6,015	7,663	6,150
Total ending allowance balance	8,108	9,583
Loans:
Individually evaluated for impairment	38,970	46,549	40,168
Collectively evaluated for impairment	113,440	120,573	114,601
Total loans	152,410	167,122	154,769
Loans Receivable | Residential mortgage
Allowance for loan losses:
Balance beginning of period	26,642	29,076
Charge-offs	(2,356)	(5,767)
Recoveries	209	392
Provision	2,433	3,655
Balance end of period	26,928	27,356
Ending allowance attributable to loans:
Individually evaluated for impairment	1,804	2,254	2,165
Collectively evaluated for impairment	25,124	25,102	24,477
Total ending allowance balance	26,928	27,356
Loans:
Individually evaluated for impairment	22,156	21,525	22,247
Collectively evaluated for impairment	1,223,819	1,109,723	1,191,956
Total loans	1,245,975	1,131,248	1,214,203
Loans Receivable | Residential construction
Allowance for loan losses:
Balance beginning of period	26,662	30,379
Charge-offs	(2,982)	(5,629)
Recoveries	9	315
Provision	(363)	4,408
Balance end of period	23,326	29,473
Ending allowance attributable to loans:
Individually evaluated for impairment	1,945	3,236	625
Collectively evaluated for impairment	21,381	26,237	26,037
Total ending allowance balance	23,326	29,473
Loans:
Individually evaluated for impairment	31,936	47,048	34,055
Collectively evaluated for impairment	339,797	388,327	347,622
Total loans	371,733	435,375	381,677
Loans Receivable | Consumer installment
Allowance for loan losses:
Balance beginning of period	2,747	2,124
Charge-offs	(707)	(753)
Recoveries	183	275
Provision	(131)	252
Balance end of period	2,092	1,898
Ending allowance attributable to loans:
Individually evaluated for impairment	14	63	19
Collectively evaluated for impairment	2,078	1,835	2,728
Total ending allowance balance	2,092	1,898
Loans:
Individually evaluated for impairment	407	331	430
Collectively evaluated for impairment	165,241	110,787	152,318
Total loans	165,648	111,118	152,748
Loans Receivable | Unallocated
Allowance for loan losses:
Balance beginning of period	9,313	9,467
Charge-offs
Recoveries
Provision	(48)	(262)
Balance end of period	9,265	9,205
Ending allowance attributable to loans:
Individually evaluated for impairment
Collectively evaluated for impairment	9,265	9,205	9,313
Total ending allowance balance	9,265	9,205
Loans:
Individually evaluated for impairment
Collectively evaluated for impairment
Total loans