Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses by Loan and Lease Class (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	$ 128,499	$ 112,219	$ 125,926	$ 110,784
Charge- Offs	(8,188)	(7,698)	(15,076)	(14,801)
Recoveries	1,966	1,822	3,291	3,354
Net Charge- Offs	(6,222)	(5,876)	(11,785)	(11,447)
Provision for credit losses	8,864	10,405	17,000	17,411
Balance at End of Period	131,141	116,748	131,141	116,748
Originated Loans [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	121,247	107,123	117,952	104,884
Charge- Offs	(7,720)	(5,919)	(14,467)	(12,782)
Recoveries	1,925	1,084	2,901	2,330
Net Charge- Offs	(5,795)	(4,835)	(11,566)	(10,452)
Provision for credit losses	8,744	8,900	17,810	16,756
Balance at End of Period	124,196	111,188	124,196	111,188
Acquired Loans [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	7,252	5,096	7,974	5,900
Charge- Offs	(468)	(1,779)	(609)	(2,019)
Recoveries	41	738	390	1,024
Net Charge- Offs	(427)	(1,041)	(219)	(995)
Provision for credit losses	120	1,505	(810)	655
Balance at End of Period	6,945	5,560	6,945	5,560
Commercial Real Estate [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	38,792	38,534	37,588	32,548
Charge- Offs	(977)	(1,572)	(1,978)	(3,795)
Recoveries	200	263	409	562
Net Charge- Offs	(777)	(1,309)	(1,569)	(3,233)
Provision for credit losses	1,857	1,253	3,853	9,163
Balance at End of Period	39,872	38,478	39,872	38,478
Commercial and Industrial [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	32,803	29,971	32,645	32,603
Charge- Offs	(1,416)	(540)	(2,100)	(1,053)
Recoveries	976	168	1,096	538
Net Charge- Offs	(440)	(372)	(1,004)	(515)
Provision for credit losses	(58)	3,418	664	929
Balance at End of Period	32,305	33,017	32,305	33,017
Commercial Leases [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	2,576	1,944	2,398	1,903
Charge- Offs	(111)	(63)	(204)	(150)
Recoveries	35	53	45	82
Net Charge- Offs	(76)	(10)	(159)	(68)
Provision for credit losses	(277)	145	(16)	244
Balance at End of Period	2,223	2,079	2,223	2,079
Total Commercial Loans and Leases [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	74,171	70,449	72,631	67,054
Charge- Offs	(2,504)	(2,175)	(4,282)	(4,998)
Recoveries	1,211	484	1,550	1,182
Net Charge- Offs	(1,293)	(1,691)	(2,732)	(3,816)
Provision for credit losses	1,522	4,816	4,501	10,336
Balance at End of Period	74,400	73,574	74,400	73,574
Direct Installment [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	21,204	16,630	20,538	17,824
Charge- Offs	(2,953)	(2,264)	(5,386)	(4,785)
Recoveries	297	283	566	550
Net Charge- Offs	(2,656)	(1,981)	(4,820)	(4,235)
Provision for credit losses	3,731	2,195	6,561	3,255
Balance at End of Period	22,279	16,844	22,279	16,844
Residential Mortgages [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	8,471	5,307	8,024	5,836
Charge- Offs	(112)	(137)	(623)	(269)
Recoveries	24	44	39	48
Net Charge- Offs	(88)	(93)	(584)	(221)
Provision for credit losses	196	292	1,139	(109)
Balance at End of Period	8,579	5,506	8,579	5,506
Indirect Installment [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	7,657	6,500	7,504	6,409
Charge- Offs	(1,503)	(696)	(2,783)	(1,498)
Recoveries	332	230	634	447
Net Charge- Offs	(1,171)	(466)	(2,149)	(1,051)
Provision for credit losses	2,423	659	3,554	1,335
Balance at End of Period	8,909	6,693	8,909	6,693
Consumer Lines of Credit [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	8,890	7,658	8,496	7,231
Charge- Offs	(323)	(340)	(733)	(663)
Recoveries	36	38	76	93
Net Charge- Offs	(287)	(302)	(657)	(570)
Provision for credit losses	515	308	1,279	1,003
Balance at End of Period	9,118	7,664	9,118	7,664
Other [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	854	579	759	530
Charge- Offs	(325)	(307)	(660)	(569)
Recoveries	25	5	36	10
Net Charge- Offs	(300)	(302)	(624)	(559)
Provision for credit losses	357	630	776	936
Balance at End of Period	911	907	911	907
Purchased Credit-Impaired Loans [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	621	708	660	1,000
Charge- Offs		(1,653)	(64)	(1,902)
Recoveries			19
Net Charge- Offs		(1,653)	(45)	(1,902)
Provision for credit losses	37	1,393	43	1,350
Balance at End of Period	658	448	658	448
Other Acquired Loans [Member]
Schedule Of Allowance For Loan Losses [Line Items]
Balance at Beginning of Period	6,631	4,388	7,314	4,900
Charge- Offs	(468)	(126)	(545)	(117)
Recoveries	41	738	371	1,024
Net Charge- Offs	(427)	612	(174)	907
Provision for credit losses	83	112	(853)	(695)
Balance at End of Period	$ 6,287	$ 5,112	$ 6,287	$ 5,112