Loans, Allowance for Credit Losses, and Credit Quality Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2015	Dec. 31, 2014
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	$ 266,302	$ 268,315
Provision for loan losses	18,500	13,000
Charge offs	(39,539)	(44,096)
Recoveries	17,273	29,083
Loans and Leases Receivable, Allowance, Ending Balance	262,536	266,302
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			$ 6,293	$ 17,866
Ending balance impaired loans collectively evaluated for impairment			25,420	32,565
Total impaired loans			31,713	50,431
Ending balance all other loans collectively evaluated for impairment			230,823	215,871
Total	266,302	268,315	262,536	266,302
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			78,954	101,822
Ending balance impaired loans collectively evaluated for impairment			151,309	173,807
Total impaired loans			230,263	275,629
Ending balance all other loans collectively evaluated for impairment			18,294,510	17,318,217
Total loans			18,524,773	17,593,846
Commercial and Industrial [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	116,025	104,501
Provision for loan losses	15,749	14,767
Charge offs	(19,672)	(14,633)
Recoveries	6,392	11,390
Loans and Leases Receivable, Allowance, Ending Balance	118,494	116,025
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			5,922	13,615
Ending balance impaired loans collectively evaluated for impairment			977	2,852
Total impaired loans			6,899	16,467
Ending balance all other loans collectively evaluated for impairment			111,595	99,558
Total	116,025	104,501	118,494	116,025
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			55,148	45,118
Ending balance impaired loans collectively evaluated for impairment			31,871	38,437
Total impaired loans			87,019	83,555
Ending balance all other loans collectively evaluated for impairment			5,998,454	5,822,347
Total loans			6,085,473	5,905,902
Commercial Real Estate Owner Occupied [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	16,510	19,476
Provision for loan losses	7,245	(1,296)
Charge offs	(2,325)	(3,476)
Recoveries	892	1,806
Loans and Leases Receivable, Allowance, Ending Balance	22,322	16,510
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	1,490
Ending balance impaired loans collectively evaluated for impairment			571	1,731
Total impaired loans			571	3,221
Ending balance all other loans collectively evaluated for impairment			21,751	13,289
Total	16,510	19,476	22,322	16,510
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			11,174	20,731
Ending balance impaired loans collectively evaluated for impairment			9,537	15,548
Total impaired loans			20,711	36,279
Ending balance all other loans collectively evaluated for impairment			945,978	971,658
Total loans			966,689	1,007,937
Lease Financing [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	1,610	1,607
Provision for loan losses	(835)	35
Charge offs	0	(39)
Recoveries	0	7
Loans and Leases Receivable, Allowance, Ending Balance	775	1,610
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	574
Ending balance impaired loans collectively evaluated for impairment			0	0
Total impaired loans			0	574
Ending balance all other loans collectively evaluated for impairment			775	1,036
Total	1,610	1,607	775	1,610
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			1,763	1,801
Ending balance impaired loans collectively evaluated for impairment			0	0
Total impaired loans			1,763	1,801
Ending balance all other loans collectively evaluated for impairment			40,844	49,728
Total loans			42,607	51,529
Commercial Real Estate Investor [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	46,333	58,156
Provision for loan losses	(2,703)	(17,290)
Charge offs	(3,947)	(4,529)
Recoveries	4,124	9,996
Loans and Leases Receivable, Allowance, Ending Balance	43,807	46,333
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			197	1,649
Ending balance impaired loans collectively evaluated for impairment			1,152	1,938
Total impaired loans			1,349	3,587
Ending balance all other loans collectively evaluated for impairment			42,458	42,746
Total	46,333	58,156	43,807	46,333
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			3,822	19,683
Ending balance impaired loans collectively evaluated for impairment			21,679	26,129
Total impaired loans			25,501	45,812
Ending balance all other loans collectively evaluated for impairment			3,157,851	3,010,673
Total loans			3,183,352	3,056,485
Real Estate Construction Port Folio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	20,999	23,418
Provision for loan losses	(1,314)	(1,277)
Charge offs	(546)	(1,958)
Recoveries	1,924	816
Loans and Leases Receivable, Allowance, Ending Balance	21,063	20,999
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	328
Ending balance impaired loans collectively evaluated for impairment			474	767
Total impaired loans			474	1,095
Ending balance all other loans collectively evaluated for impairment			20,589	19,904
Total	20,999	23,418	21,063	20,999
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			0	3,776
Ending balance impaired loans collectively evaluated for impairment			1,482	2,350
Total impaired loans			1,482	6,126
Ending balance all other loans collectively evaluated for impairment			1,122,798	1,002,830
Total loans			1,124,280	1,008,956
Home Equity Portfolio [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	26,464	27,932
Provision for loan losses	(987)	6,278
Charge offs	(5,466)	(10,946)
Recoveries	2,568	3,200
Loans and Leases Receivable, Allowance, Ending Balance	22,579	26,464
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			3	11
Ending balance impaired loans collectively evaluated for impairment			9,652	11,371
Total impaired loans			9,655	11,382
Ending balance all other loans collectively evaluated for impairment			12,924	15,082
Total	26,464	27,932	22,579	26,464
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			170	962
Ending balance impaired loans collectively evaluated for impairment			20,416	23,698
Total impaired loans			20,586	24,660
Ending balance all other loans collectively evaluated for impairment			993,879	1,027,267
Total loans			1,014,465	1,051,927
Installment and Credit Cards Portfolio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	6,435	2,416
Provision for loan losses	1,284	6,279
Charge offs	(2,934)	(2,876)
Recoveries	569	616
Loans and Leases Receivable, Allowance, Ending Balance	5,354	6,435
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	0
Ending balance impaired loans collectively evaluated for impairment			210	308
Total impaired loans			210	308
Ending balance all other loans collectively evaluated for impairment			5,144	6,127
Total	6,435	2,416	5,354	6,435
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			0	0
Ending balance impaired loans collectively evaluated for impairment			1,190	1,587
Total impaired loans			1,190	1,587
Ending balance all other loans collectively evaluated for impairment			424,539	452,632
Total loans			425,729	454,219
Residential Portfolio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	31,926	30,809
Provision for loan losses	61	5,504
Charge offs	(4,649)	(5,639)
Recoveries	804	1,252
Loans and Leases Receivable, Allowance, Ending Balance	28,142	31,926
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			171	199
Ending balance impaired loans collectively evaluated for impairment			12,384	13,598
Total impaired loans			12,555	13,797
Ending balance all other loans collectively evaluated for impairment			15,587	18,129
Total	$ 31,926	$ 30,809	28,142	31,926
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			6,877	9,751
Ending balance impaired loans collectively evaluated for impairment			65,134	66,058
Total impaired loans			72,011	75,809
Ending balance all other loans collectively evaluated for impairment			5,610,167	4,981,082
Total loans			$ 5,682,178	$ 5,056,891