Business Segments - Financial Information for Segments of Corporation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest income	$ 170,931	$ 135,448	$ 326,685	$ 268,817
Interest expense	16,562	11,681	31,962	23,129
Net interest income	154,369	123,767	294,723	245,688
Provision for credit losses	16,640	8,864	28,408	17,000
Non-interest income	51,411	39,752	97,455	77,934
Non-interest expense	126,241	94,500	260,240	187,040
Intangible amortization	3,388	1,999	6,037	4,114
Income tax expense (benefit)	18,211	18,025	30,061	34,994
Net income (loss)	41,300	40,131	67,432	80,474
Total assets	21,214,967	16,598,601	21,214,967	16,598,601	$ 17,557,662
Total intangibles	1,104,991	876,390	1,104,991	876,390
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	158,900	123,967	302,878	246,085
Interest expense	13,768	10,166	26,362	20,107
Net interest income	145,132	113,801	276,516	225,978
Provision for credit losses	14,398	6,945	24,315	13,272
Non-interest income	39,514	28,313	70,747	55,614
Non-interest expense	109,786	78,339	227,834	155,418
Intangible amortization	3,180	1,830	5,621	3,777
Income tax expense (benefit)	17,284	17,009	27,401	32,940
Net income (loss)	39,998	37,991	62,092	76,185
Total assets	21,027,436	16,412,240	21,027,436	16,412,240
Total intangibles	1,080,385	851,250	1,080,385	851,250
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Non-interest income	9,183	9,199	17,999	17,586
Non-interest expense	6,960	6,931	14,049	13,424
Intangible amortization	64	68	129	136
Income tax expense (benefit)	782	789	1,387	1,447
Net income (loss)	1,377	1,411	2,434	2,579
Total assets	20,044	21,255	20,044	21,255
Total intangibles	10,318	10,584	10,318	10,584
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	21	22	43	45
Net interest income	21	22	43	45
Non-interest income	3,268	2,753	7,462	6,346
Non-interest expense	3,276	3,581	6,577	7,751
Intangible amortization	144	101	287	201
Income tax expense (benefit)	(41)	(312)	234	(538)
Net income (loss)	(90)	(595)	407	(1,023)
Total assets	22,732	22,523	22,732	22,523
Total intangibles	12,479	12,747	12,479	12,747
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	10,126	9,778	19,911	19,371
Interest expense	930	855	1,871	1,715
Net interest income	9,196	8,923	18,040	17,656
Provision for credit losses	1,472	1,964	2,998	3,538
Non-interest income	754	732	1,470	1,408
Non-interest expense	5,372	4,994	10,576	9,802
Income tax expense (benefit)	1,208	1,038	2,320	2,187
Net income (loss)	1,898	1,659	3,616	3,537
Total assets	196,603	186,134	196,603	186,134
Total intangibles	1,809	1,809	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	1,884	1,681	3,853	3,316
Interest expense	1,864	660	3,729	1,307
Net interest income	20	1,021	124	2,009
Provision for credit losses	770	(45)	1,095	190
Non-interest income	(1,308)	(1,245)	(223)	(3,020)
Non-interest expense	847	655	1,204	645
Income tax expense (benefit)	(1,022)	(499)	(1,281)	(1,042)
Net income (loss)	(1,883)	(335)	(1,117)	(804)
Total assets	$ (51,848)	$ (43,551)	$ (51,848)	$ (43,551)