Impaired Loans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	$ 34,317	$ 45,688
Loans with a specific valuation allowance, Unpaid principal balance	35,663	48,477
Specific valuation allowance	10,324	11,597
Loans with a specific valuation allowance, Average balance	40,003	53,339
Loans without a specific valuation allowance, Recorded balance	128,229	115,678
Loans without a specific valuation allowance, Unpaid principal balance	157,666	145,038
Loans without a specific valuation allowance, Average balance	121,953	128,645
Recorded balance	162,546	161,366
Unpaid principal balance	193,329	193,515
Average balance	161,956	181,984
Residential Real Estate
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	5,107	4,110
Loans with a specific valuation allowance, Unpaid principal balance	5,187	4,276
Specific valuation allowance	1,262	853
Loans with a specific valuation allowance, Average balance	4,608	5,480
Loans without a specific valuation allowance, Recorded balance	13,907	15,466
Loans without a specific valuation allowance, Unpaid principal balance	15,230	16,683
Loans without a specific valuation allowance, Average balance	14,686	15,580
Recorded balance	19,014	19,576
Unpaid principal balance	20,417	20,959
Average balance	19,294	21,060
Commercial Real Estate
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	12,957	27,155
Loans with a specific valuation allowance, Unpaid principal balance	13,561	28,048
Specific valuation allowance	2,426	2,967
Loans with a specific valuation allowance, Average balance	20,056	24,519
Loans without a specific valuation allowance, Recorded balance	85,509	78,109
Loans without a specific valuation allowance, Unpaid principal balance	107,444	100,266
Loans without a specific valuation allowance, Average balance	81,809	89,015
Recorded balance	98,466	105,264
Unpaid principal balance	121,005	128,314
Average balance	101,865	113,534
Other Commercial
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	14,144	11,377
Loans with a specific valuation allowance, Unpaid principal balance	14,297	12,461
Specific valuation allowance	5,974	6,836
Loans with a specific valuation allowance, Average balance	12,761	19,874
Loans without a specific valuation allowance, Recorded balance	20,492	13,944
Loans without a specific valuation allowance, Unpaid principal balance	25,912	19,117
Loans without a specific valuation allowance, Average balance	17,218	14,024
Recorded balance	34,636	25,321
Unpaid principal balance	40,209	31,578
Average balance	29,979	33,898
Home Equity
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	403	1,214
Loans with a specific valuation allowance, Unpaid principal balance	419	1,336
Specific valuation allowance	172	447
Loans with a specific valuation allowance, Average balance	809	1,039
Loans without a specific valuation allowance, Recorded balance	6,094	5,687
Loans without a specific valuation allowance, Unpaid principal balance	6,789	6,403
Loans without a specific valuation allowance, Average balance	5,891	7,163
Recorded balance	6,497	6,901
Unpaid principal balance	7,208	7,739
Average balance	6,700	8,202
Other Consumer
Summary of the impaired loans by portfolio class of loans
Loans with a specific valuation allowance, Recorded balance	1,706	1,832
Loans with a specific valuation allowance, Unpaid principal balance	2,199	2,356
Specific valuation allowance	490	494
Loans with a specific valuation allowance, Average balance	1,769	2,427
Loans without a specific valuation allowance, Recorded balance	2,227	2,472
Loans without a specific valuation allowance, Unpaid principal balance	2,291	2,569
Loans without a specific valuation allowance, Average balance	2,349	2,863
Recorded balance	3,933	4,304
Unpaid principal balance	4,490	4,925
Average balance	$ 4,118	$ 5,290