Business Segments - Financial Information for Segments of Corporation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Interest income	$ 124,440	$ 107,841	$ 242,320	$ 212,959
Interest expense	10,248	11,095	20,303	23,117
Net interest income	114,192	96,746	222,017	189,842
Provision for loan losses	10,405	7,903	17,411	15,444
Non-interest income	39,190	36,697	81,260	70,309
Non-interest expense	90,123	82,056	182,006	158,933
Intangible amortization	2,461	2,071	4,744	3,996
Income tax expense (benefit)	15,562	12,220	29,761	24,047
Net income (loss)	34,831	29,193	69,355	57,731
Total assets	15,019,247	12,573,391	15,019,247	12,573,391	13,563,405
Total intangibles	853,806	746,980	853,806	746,980
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	113,161	97,217	219,852	191,268
Interest expense	8,730	7,979	16,978	16,897
Net interest income	104,431	89,238	202,874	174,371
Provision for loan losses	8,425	6,031	13,721	11,851
Non-interest income	27,420	25,940	59,333	49,638
Non-interest expense	75,281	67,336	152,147	130,304
Intangible amortization	2,288	1,893	4,398	3,641
Income tax expense (benefit)	14,048	11,762	27,391	22,934
Net income (loss)	31,809	28,156	64,550	55,279
Total assets	14,842,988	12,387,990	14,842,988	12,387,990
Total intangibles	830,809	723,282	830,809	723,282
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Interest income
Interest expense
Net interest income
Provision for loan losses
Non-interest income	8,033	7,263	15,356	14,378
Non-interest expense	6,452	6,402	12,744	12,488
Intangible amortization	72	76	144	152
Income tax expense (benefit)	548	293	899	643
Net income (loss)	961	492	1,569	1,095
Total assets	21,828	19,201	21,828	19,201
Total intangibles	10,864	11,160	10,864	11,160
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	25	27	50	55
Interest expense
Net interest income	25	27	50	55
Provision for loan losses
Non-interest income	2,999	3,243	7,209	6,802
Non-interest expense	2,911	2,810	5,957	5,621
Intangible amortization	101	102	202	203
Income tax expense (benefit)	8	130	393	369
Net income (loss)	4	228	707	664
Total assets	20,785	20,666	20,785	20,666
Total intangibles	10,324	10,729	10,324	10,729
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	9,578	9,304	18,943	18,320
Interest expense	809	838	1,655	1,694
Net interest income	8,769	8,466	17,288	16,626
Provision for loan losses	1,778	1,678	3,235	3,205
Non-interest income	741	719	1,401	1,348
Non-interest expense	4,880	4,823	9,817	9,339
Intangible amortization
Income tax expense (benefit)	1,097	1,041	2,170	2,089
Net income (loss)	1,755	1,643	3,467	3,341
Total assets	182,401	179,396	182,401	179,396
Total intangibles	1,809	1,809	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	1,676	1,293	3,475	3,316
Interest expense	709	2,278	1,670	4,526
Net interest income	967	(985)	1,805	(1,210)
Provision for loan losses	202	194	455	388
Non-interest income	(3)	(468)	(2,039)	(1,857)
Non-interest expense	599	685	1,341	1,181
Intangible amortization
Income tax expense (benefit)	(139)	(1,006)	(1,092)	(1,988)
Net income (loss)	302	(1,326)	(938)	(2,648)
Total assets	(48,755)	(33,862)	(48,755)	(33,862)
Total intangibles