Loans, Allowance for Loan and Lease Losses, and Reserve for Off-Balance Sheet Credit Commitments (Detail 4) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Allowance for Loan and Lease Losses
Beginning Balance	$ 316,922	$ 311,276	$ 310,149	$ 302,584
Charge-offs	(4,816)	(3,849)	(11,024)	(19,510)
Recoveries	10,999	14,399	16,193	30,595
Net recoveries (charge-offs)	6,183	10,550	5,169	11,085
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(6,000)	(8,000)	4,000	(9,000)
Transfers from (to) reserve for off-balance sheet credit commitments	52	(1,123)	(2,161)	8,034
Ending Balance	317,157	312,703	317,157	312,703
Allowance individually evaluated for impairment	2,609	1,595	2,609	1,595
Allowance collectively evaluated for impairment	314,548	311,108	314,548	311,108
Loans and leases, excluding acquired impaired loans	22,536,584	19,347,988	22,536,584	19,347,988	$ 20,337,206
Loans and leases, individually evaluated for impairment	59,892	58,575	59,892	58,575
Loans and leases, collectively evaluated for impairment	22,476,692	19,289,413	22,476,692	19,289,413
Reserve for Off Balance Sheet Credit Commitments
Balance, beginning of the year	30,024	24,787	27,811	33,944
Transfers (to) from allowance for loan and lease losses	(52)	1,123	2,161	(8,034)
Balance, end of the year	29,972	25,910	29,972	25,910
Commercial (includes lease financing)
Allowance for Loan and Lease Losses
Beginning Balance	124,314	126,279	115,855	117,103
Charge-offs	(4,576)	(3,773)	(10,276)	(18,594)
Recoveries	10,514	6,202	12,229	15,437
Net recoveries (charge-offs)	5,938	2,429	1,953	(3,157)
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	2,939	(5,762)	15,383	(353)
Transfers from (to) reserve for off-balance sheet credit commitments				9,353
Ending Balance	133,191	122,946	133,191	122,946
Allowance individually evaluated for impairment	2,315	1,304	2,315	1,304
Allowance collectively evaluated for impairment	130,876	121,642	130,876	121,642
Loans and leases, excluding acquired impaired loans	10,941,277	9,236,294	10,941,277	9,236,294
Loans and leases, individually evaluated for impairment	18,185	16,316	18,185	16,316
Loans and leases, collectively evaluated for impairment	10,923,092	9,219,978	10,923,092	9,219,978
Commercial real estate mortgages
Allowance for Loan and Lease Losses
Beginning Balance	48,649	50,651	44,745	50,678
Charge-offs				(5)
Recoveries	68	225	1,270	352
Net recoveries (charge-offs)	68	225	1,270	347
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(211)	113	2,491	(36)
Ending Balance	48,506	50,989	48,506	50,989
Allowance individually evaluated for impairment	255	291	255	291
Allowance collectively evaluated for impairment	48,251	50,698	48,251	50,698
Loans and leases, excluding acquired impaired loans	3,947,746	3,565,188	3,947,746	3,565,188	3,539,703
Loans and leases, individually evaluated for impairment	22,918	25,551	22,918	25,551
Loans and leases, collectively evaluated for impairment	3,924,828	3,539,637	3,924,828	3,539,637
Residential mortgages
Allowance for Loan and Lease Losses
Beginning Balance	9,660	10,296	10,296	11,540
Charge-offs				(482)
Recoveries	34	33	110	258
Net recoveries (charge-offs)	34	33	110	(224)
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	154	1,138	(558)	151
Ending Balance	9,848	11,467	9,848	11,467
Allowance individually evaluated for impairment	39		39
Allowance collectively evaluated for impairment	9,809	11,467	9,809	11,467
Loans and leases, excluding acquired impaired loans	5,709,272	5,023,213	5,709,272	5,023,213	5,106,803
Loans and leases, individually evaluated for impairment	11,850	7,785	11,850	7,785
Loans and leases, collectively evaluated for impairment	5,697,422	5,015,428	5,697,422	5,015,428
Real estate construction
Allowance for Loan and Lease Losses
Beginning Balance	10,652	7,191	9,115	6,351
Recoveries	142	7,729	1,852	12,804
Net recoveries (charge-offs)	142	7,729	1,852	12,804
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	783	(6,175)	610	(10,410)
Ending Balance	11,577	8,745	11,577	8,745
Allowance collectively evaluated for impairment	11,577	8,745	11,577	8,745
Loans and leases, excluding acquired impaired loans	932,422	585,232	932,422	585,232	710,224
Loans and leases, individually evaluated for impairment	5,802	6,610	5,802	6,610
Loans and leases, collectively evaluated for impairment	926,620	578,622	926,620	578,622
Home equity loans and lines of credit
Allowance for Loan and Lease Losses
Beginning Balance	5,404	6,575	6,609	6,677
Charge-offs				(165)
Recoveries	37	52	110	254
Net recoveries (charge-offs)	37	52	110	89
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(163)	401	(1,441)	262
Ending Balance	5,278	7,028	5,278	7,028
Allowance collectively evaluated for impairment	5,278	7,028	5,278	7,028
Loans and leases, excluding acquired impaired loans	799,711	759,258	799,711	759,258	785,796
Loans and leases, individually evaluated for impairment	1,137	2,313	1,137	2,313
Loans and leases, collectively evaluated for impairment	798,574	756,945	798,574	756,945
Installment
Allowance for Loan and Lease Losses
Beginning Balance	2,208	2,284	2,228	1,842
Charge-offs	(240)	(76)	(748)	(264)
Recoveries	204	158	622	1,490
Net recoveries (charge-offs)	(36)	82	(126)	1,226
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	118	18	188	(684)
Ending Balance	2,290	2,384	2,290	2,384
Allowance collectively evaluated for impairment	2,290	2,384	2,290	2,384
Loans and leases, excluding acquired impaired loans	206,156	178,803	206,156	178,803	$ 184,613
Loans and leases, collectively evaluated for impairment	206,156	178,803	206,156	178,803
Qualitative
Allowance for Loan and Lease Losses
Beginning Balance	116,035	108,000	121,301	108,393
(Reversal of) provision for credit losses on loans and leases, excluding acquired impaired loans	(9,620)	2,267	(12,673)	2,070
Transfers from (to) reserve for off-balance sheet credit commitments	52	(1,123)	(2,161)	(1,319)
Ending Balance	106,467	109,144	106,467	109,144
Allowance collectively evaluated for impairment	$ 106,467	$ 109,144	$ 106,467	$ 109,144