Segment Information - Schedule of Financial Information Concerning Segments (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]
Net interest income	$ 84,482	$ 79,191	$ 167,960	$ 158,241
Noninterest income	39,653	46,244	80,216	92,559
Noncash items:
Depreciation and software amortization	3,521	2,909	6,913	5,656
Provision for loan losses	(400)	(3,693)	(363)	(2,848)
Amortization of intangibles	2,003	1,840	3,840	4,365
Income tax expense (benefit)	7,658	13,734	16,900	24,126
Segment profit	18,773	28,478	45,283	52,423
Segment assets	10,387,933	9,641,071	10,387,933	9,641,071	9,581,744
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	84,726	79,291	168,270	158,491
Noninterest income	21,760	29,704	44,061	58,844
Noncash items:
Depreciation and software amortization	3,338	2,794	6,569	5,436
Provision for loan losses	(400)	(3,693)	(363)	(2,848)
Amortization of intangibles	1,325	1,177	2,585	3,065
Income tax expense (benefit)	6,853	14,031	17,712	24,447
Segment profit	22,202	28,372	45,037	52,107
Segment assets	10,233,398	9,492,552	10,233,398	9,492,552
Insurance [Member]
Segment Reporting Information [Line Items]
Net interest income	3	5	6	10
Noninterest income	9,788	9,473	21,764	20,337
Noncash items:
Depreciation and software amortization	35	37	70	71
Amortization of intangibles	413	478	820	928
Income tax expense (benefit)	165	18	968	705
Segment profit	240	370	2,113	1,421
Segment assets	62,800	61,831	62,800	61,831
Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest income	11	12	21	23
Noninterest income	7,668	6,576	13,627	12,403
Noncash items:
Depreciation and software amortization	13	5	18	12
Amortization of intangibles	265	185	435	372
Income tax expense (benefit)	109	355	474	672
Segment profit	120	587	786	1,078
Segment assets	20,015	14,119	20,015	14,119
Other [Member]
Segment Reporting Information [Line Items]
Net interest income	(258)	(117)	(337)	(283)
Noninterest income	437	491	764	975
Noncash items:
Depreciation and software amortization	135	73	256	137
Income tax expense (benefit)	531	(670)	(2,254)	(1,698)
Segment profit	(3,789)	(851)	(2,653)	(2,183)
Segment assets	$ 71,720	$ 72,569	$ 71,720	$ 72,569