Loans, Allowance for Credit Losses, and Credit Quality Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 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	9,500	13,000
Charge offs	(27,807)	(44,096)
Recoveries	13,543	29,083
Loans and Leases Receivable, Allowance, Ending Balance	261,538	266,302
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			$ 7,520	$ 17,866
Ending balance impaired loans collectively evaluated for impairment			27,305	32,565
Total impaired loans			34,825	50,431
Ending balance all other loans collectively evaluated for impairment			226,713	215,871
Total	266,302	268,315	261,538	266,302
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			94,524	101,822
Ending balance impaired loans collectively evaluated for impairment			156,057	173,807
Total impaired loans			250,581	275,629
Ending balance all other loans collectively evaluated for impairment			18,052,671	17,318,217
Total loans			18,303,252	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	7,855	14,767
Charge offs	(13,012)	(14,633)
Recoveries	4,441	11,390
Loans and Leases Receivable, Allowance, Ending Balance	115,309	116,025
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			6,381	13,615
Ending balance impaired loans collectively evaluated for impairment			1,415	2,852
Total impaired loans			7,796	16,467
Ending balance all other loans collectively evaluated for impairment			107,513	99,558
Total	116,025	104,501	115,309	116,025
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			62,483	45,118
Ending balance impaired loans collectively evaluated for impairment			34,318	38,437
Total impaired loans			96,801	83,555
Ending balance all other loans collectively evaluated for impairment			6,111,391	5,822,347
Total loans			6,208,192	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	4,583	(1,296)
Charge offs	(2,249)	(3,476)
Recoveries	312	1,806
Loans and Leases Receivable, Allowance, Ending Balance	19,156	16,510
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			455	1,490
Ending balance impaired loans collectively evaluated for impairment			587	1,731
Total impaired loans			1,042	3,221
Ending balance all other loans collectively evaluated for impairment			18,114	13,289
Total	16,510	19,476	19,156	16,510
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			16,485	20,731
Ending balance impaired loans collectively evaluated for impairment			7,769	15,548
Total impaired loans			24,254	36,279
Ending balance all other loans collectively evaluated for impairment			953,929	971,658
Total loans			978,183	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	(128)	35
Charge offs	0	(39)
Recoveries	0	7
Loans and Leases Receivable, Allowance, Ending Balance	1,482	1,610
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			464	574
Ending balance impaired loans collectively evaluated for impairment			0	0
Total impaired loans			464	574
Ending balance all other loans collectively evaluated for impairment			1,018	1,036
Total	1,610	1,607	1,482	1,610
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			1,656	1,801
Ending balance impaired loans collectively evaluated for impairment			0	0
Total impaired loans			1,656	1,801
Ending balance all other loans collectively evaluated for impairment			45,244	49,728
Total loans			46,900	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	(3,199)	(17,290)
Charge offs	(3,430)	(4,529)
Recoveries	4,103	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			44	1,649
Ending balance impaired loans collectively evaluated for impairment			1,911	1,938
Total impaired loans			1,955	3,587
Ending balance all other loans collectively evaluated for impairment			41,852	42,746
Total	46,333	58,156	43,807	46,333
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			2,914	19,683
Ending balance impaired loans collectively evaluated for impairment			25,185	26,129
Total impaired loans			28,099	45,812
Ending balance all other loans collectively evaluated for impairment			3,098,341	3,010,673
Total loans			3,126,440	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	(530)	(1,277)
Charge offs	(447)	(1,958)
Recoveries	1,863	816
Loans and Leases Receivable, Allowance, Ending Balance	21,885	20,999
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	328
Ending balance impaired loans collectively evaluated for impairment			518	767
Total impaired loans			518	1,095
Ending balance all other loans collectively evaluated for impairment			21,367	19,904
Total	20,999	23,418	21,885	20,999
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			1,925	3,776
Ending balance impaired loans collectively evaluated for impairment			1,695	2,350
Total impaired loans			3,620	6,126
Ending balance all other loans collectively evaluated for impairment			1,088,688	1,002,830
Total loans			1,092,308	1,008,956
Home Equity Portfolio [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	30,359	32,196
Provision for loan losses	(319)	7,087
Charge offs	(4,387)	(12,332)
Recoveries	1,849	3,408
Loans and Leases Receivable, Allowance, Ending Balance	27,502	30,359
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			3	11
Ending balance impaired loans collectively evaluated for impairment			11,398	13,004
Total impaired loans			11,401	13,015
Ending balance all other loans collectively evaluated for impairment			16,101	17,344
Total	30,359	32,196	27,502	30,359
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			321	962
Ending balance impaired loans collectively evaluated for impairment			27,686	30,845
Total impaired loans			28,007	31,807
Ending balance all other loans collectively evaluated for impairment			1,502,456	1,604,251
Total loans			1,530,463	1,636,058
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	1,214	6,279
Charge offs	(1,928)	(2,876)
Recoveries	373	616
Loans and Leases Receivable, Allowance, Ending Balance	6,094	6,435
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			0	0
Ending balance impaired loans collectively evaluated for impairment			234	308
Total impaired loans			234	308
Ending balance all other loans collectively evaluated for impairment			5,860	6,127
Total	6,435	2,416	6,094	6,435
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			0	0
Ending balance impaired loans collectively evaluated for impairment			1,250	1,587
Total impaired loans			1,250	1,587
Ending balance all other loans collectively evaluated for impairment			429,573	452,632
Total loans			430,823	454,219
Residential Portfolio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Loans and Leases Receivable, Allowance, Beginning Balance	28,031	26,545
Provision for loan losses	24	4,695
Charge offs	(2,354)	(4,253)
Recoveries	602	1,044
Loans and Leases Receivable, Allowance, Ending Balance	26,303	28,031
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment			173	199
Ending balance impaired loans collectively evaluated for impairment			11,242	11,965
Total impaired loans			11,415	12,164
Ending balance all other loans collectively evaluated for impairment			14,888	15,867
Total	$ 28,031	$ 26,545	26,303	28,031
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment			8,740	9,751
Ending balance impaired loans collectively evaluated for impairment			58,154	58,911
Total impaired loans			66,894	68,662
Ending balance all other loans collectively evaluated for impairment			4,823,049	4,404,098
Total loans			$ 4,889,943	$ 4,472,760