Loans, Allowance for Credit Losses, and Credit Quality Changes in the Allowance for Loan Losses by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 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	4,500us-gaap_ProvisionForLoanAndLeaseLosses	13,000us-gaap_ProvisionForLoanAndLeaseLosses
Charge offs	(13,270)	(44,096)
Recoveries	7,736	29,083
Loans and Leases Receivable, Allowance, Ending Balance	265,268	266,302
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	8,176	17,866
Ending balance impaired loans collectively evaluated for impairment	29,210	32,565
Total impaired loans	37,386	50,431
Ending balance all other loans collectively evaluated for impairment	227,882	215,871
Total	265,268	266,302
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	101,756	101,822
Ending balance impaired loans collectively evaluated for impairment	161,407	173,807
Total impaired loans	263,163	275,629
Ending balance all other loans collectively evaluated for impairment	17,715,869us-gaap_NotesReceivableNet	17,318,217us-gaap_NotesReceivableNet
Total loans	17,979,032	17,593,846
Commercial and Industrial Portfolio Segment [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	6,836	14,767
Charge offs	(6,829)	(14,633)
Recoveries	2,179	11,390
Loans and Leases Receivable, Allowance, Ending Balance	118,211	116,025
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	5,591	13,615
Ending balance impaired loans collectively evaluated for impairment	2,038	2,852
Total impaired loans	7,629	16,467
Ending balance all other loans collectively evaluated for impairment	110,582	99,558
Total	118,211	116,025
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	58,091	45,118
Ending balance impaired loans collectively evaluated for impairment	29,995	38,437
Total impaired loans	88,086	83,555
Ending balance all other loans collectively evaluated for impairment	6,052,334	5,822,347
Total loans	6,140,420	5,905,902
Commercial Real Estate Owner Occupied Portfolio [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	3,753	(1,296)
Charge offs	(879)	(3,476)
Recoveries	140	1,806
Loans and Leases Receivable, Allowance, Ending Balance	19,524	16,510
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	910	1,490
Ending balance impaired loans collectively evaluated for impairment	1,149	1,731
Total impaired loans	2,059	3,221
Ending balance all other loans collectively evaluated for impairment	17,465	13,289
Total	19,524	16,510
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	17,133	20,731
Ending balance impaired loans collectively evaluated for impairment	14,508	15,548
Total impaired loans	31,641	36,279
Ending balance all other loans collectively evaluated for impairment	972,244	971,658
Total loans	1,003,885	1,007,937
Finance Leases Portfolio Segment [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	(130)	35
Charge offs	0	(39)
Recoveries	0	7
Loans and Leases Receivable, Allowance, Ending Balance	1,480	1,610
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	510	574
Ending balance impaired loans collectively evaluated for impairment	0	0
Total impaired loans	510	574
Ending balance all other loans collectively evaluated for impairment	970	1,036
Total	1,480	1,610
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	1,720	1,801
Ending balance impaired loans collectively evaluated for impairment	0	0
Total impaired loans	1,720	1,801
Ending balance all other loans collectively evaluated for impairment	47,776	49,728
Total loans	49,496	51,529
Commercial Real Estate Investor Portfolio Segment [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	(4,503)	(17,290)
Charge offs	(1,002)	(4,529)
Recoveries	3,531	9,996
Loans and Leases Receivable, Allowance, Ending Balance	44,359	46,333
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	689	1,649
Ending balance impaired loans collectively evaluated for impairment	1,339	1,938
Total impaired loans	2,028	3,587
Ending balance all other loans collectively evaluated for impairment	42,331	42,746
Total	44,359	46,333
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	10,297	19,683
Ending balance impaired loans collectively evaluated for impairment	26,220	26,129
Total impaired loans	36,517	45,812
Ending balance all other loans collectively evaluated for impairment	3,050,463	3,010,673
Total loans	3,086,980	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	(402)	(1,277)
Charge offs	0	(1,958)
Recoveries	743	816
Loans and Leases Receivable, Allowance, Ending Balance	21,340	20,999
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	240	328
Ending balance impaired loans collectively evaluated for impairment	801	767
Total impaired loans	1,041	1,095
Ending balance all other loans collectively evaluated for impairment	20,299	19,904
Total	21,340	20,999
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	3,843	3,776
Ending balance impaired loans collectively evaluated for impairment	2,297	2,350
Total impaired loans	6,140	6,126
Ending balance all other loans collectively evaluated for impairment	1,013,431	1,002,830
Total loans	1,019,571	1,008,956
Home Equity Port Folio Segments [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	348	7,087
Charge offs	(2,674)	(12,332)
Recoveries	669	3,408
Loans and Leases Receivable, Allowance, Ending Balance	28,702	30,359
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	10	11
Ending balance impaired loans collectively evaluated for impairment	12,350	13,004
Total impaired loans	12,360	13,015
Ending balance all other loans collectively evaluated for impairment	16,342	17,344
Total	28,702	30,359
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	911	962
Ending balance impaired loans collectively evaluated for impairment	29,255	30,845
Total impaired loans	30,166	31,807
Ending balance all other loans collectively evaluated for impairment	1,553,448	1,604,251
Total loans	1,583,614	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	359	6,279
Charge offs	(938)	(2,876)
Recoveries	169	616
Loans and Leases Receivable, Allowance, Ending Balance	6,025	6,435
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	0	0
Ending balance impaired loans collectively evaluated for impairment	264	308
Total impaired loans	264	308
Ending balance all other loans collectively evaluated for impairment	5,761	6,127
Total	6,025	6,435
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	0	0
Ending balance impaired loans collectively evaluated for impairment	1,406	1,587
Total impaired loans	1,406	1,587
Ending balance all other loans collectively evaluated for impairment	435,086	452,632
Total loans	436,492	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	(1,761)	4,695
Charge offs	(948)	(4,253)
Recoveries	305	1,044
Loans and Leases Receivable, Allowance, Ending Balance	25,627	28,031
Allowance for loan losses:
Ending balance impaired loans individually evaluated for impairment	226	199
Ending balance impaired loans collectively evaluated for impairment	11,269	11,965
Total impaired loans	11,495	12,164
Ending balance all other loans collectively evaluated for impairment	14,132	15,867
Total	25,627	28,031
Loans [Abstract]
Ending balance impaired loans individually evaluated for impairment	9,761	9,751
Ending balance impaired loans collectively evaluated for impairment	57,726	58,911
Total impaired loans	67,487	68,662
Ending balance all other loans collectively evaluated for impairment	4,591,087	4,404,098
Total loans	$ 4,658,574	$ 4,472,760

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A valuation allowance for financing receivables that are expected to be uncollectible.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of allowance for credit losses related to recorded investment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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Amount of expense related to estimated loss from loan and lease transactions.

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