Business Segments - Financial Information for Segments of Corporation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Interest income	$ 109,790	$ 107,756	$ 322,749	$ 324,328
Interest expense	10,536	14,225	33,653	45,395
Net interest income	99,254	93,531	289,096	278,933
Provision for loan losses	7,280	8,429	22,724	22,028
Non-interest income	32,858	34,813	103,282	99,336
Non-interest expense	81,106	74,840	240,039	235,345
Intangible amortization	2,115	2,242	6,226	6,892
Income tax expense (benefit)	9,977	12,090	34,024	32,549
Net income (loss)	31,634	30,743	89,365	81,455
Total assets	12,790,279	11,984,891	12,790,279	11,984,891	12,023,976
Total intangibles	748,909	717,263	748,909	717,263
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	98,716	97,364	289,984	293,756
Interest expense	7,552	10,912	24,449	35,130
Net interest income	91,164	86,452	265,535	258,626
Provision for loan losses	5,432	6,826	17,283	17,215
Non-interest income	24,365	25,048	74,118	72,904
Non-interest expense	68,091	61,820	198,395	196,510
Intangible amortization	1,938	2,056	5,694	6,334
Income tax expense (benefit)	9,552	11,456	32,486	31,882
Net income (loss)	30,516	29,342	85,795	79,589
Total assets	12,610,043	11,803,432	12,610,043	11,803,432
Total intangibles	725,389	693,029	725,389	693,029
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Interest income				4
Net interest income				4
Non-interest income	6,916	6,006	21,294	17,889
Non-interest expense	5,850	4,844	18,338	14,587
Intangible amortization	76	80	228	240
Income tax expense (benefit)	366	396	1,009	1,117
Net income (loss)	624	686	1,719	1,949
Total assets	19,614	19,075	19,614	19,075
Total intangibles	11,084	11,392	11,084	11,392
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	27	27	82	85
Net interest income	27	27	82	85
Non-interest income	3,222	3,602	10,024	10,072
Non-interest expense	2,799	2,947	8,420	8,658
Intangible amortization	101	106	304	318
Income tax expense (benefit)	128	204	497	420
Net income (loss)	221	372	885	761
Total assets	19,788	19,281	19,788	19,281
Total intangibles	10,627	11,033	10,627	11,033
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	9,600	8,860	27,920	25,888
Interest expense	839	869	2,533	2,736
Net interest income	8,761	7,991	25,387	23,152
Provision for loan losses	1,725	1,421	4,930	4,218
Non-interest income	681	590	2,029	1,674
Non-interest expense	4,724	4,829	14,063	14,016
Income tax expense (benefit)	1,145	888	3,234	2,530
Net income (loss)	1,848	1,443	5,189	4,062
Total assets	182,695	170,304	182,695	170,304
Total intangibles	1,809	1,809	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	1,447	1,505	4,763	4,595
Interest expense	2,145	2,444	6,671	7,529
Net interest income	(698)	(939)	(1,908)	(2,934)
Provision for loan losses	123	182	511	595
Non-interest income	(2,326)	(433)	(4,183)	(3,203)
Non-interest expense	(358)	400	823	1,574
Income tax expense (benefit)	(1,214)	(854)	(3,202)	(3,400)
Net income (loss)	(1,575)	(1,100)	(4,223)	(4,906)
Total assets	$ (41,861)	$ (27,201)	$ (41,861)	$ (27,201)