Business Segments - Financial Information for Segments of Corporation (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Interest income	$ 155,754	$ 133,369
Interest expense	15,400	11,448
Net interest income	140,354	121,921
Provision for credit losses	11,768	8,136
Non-interest income	46,044	38,182
Non-interest expense	133,999	92,540
Intangible amortization	2,649	2,115
Income tax expense (benefit)	11,850	16,969
Net income (loss)	26,132	40,343
Total assets	20,324,524	16,278,848	$ 17,557,662
Total intangibles	1,087,050	875,246
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	143,978	122,118
Interest expense	12,594	9,941
Net interest income	131,384	112,177
Provision for credit losses	9,917	6,327
Non-interest income	31,233	27,301
Non-interest expense	118,048	77,079
Intangible amortization	2,441	1,947
Income tax expense (benefit)	10,117	15,931
Net income (loss)	22,094	38,194
Total assets	20,151,815	16,100,851
Total intangibles	1,062,079	852,764
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Non-interest income	8,816	8,387
Non-interest expense	7,089	6,493
Intangible amortization	65	68
Income tax expense (benefit)	605	658
Net income (loss)	1,057	1,168
Total assets	20,540	21,125
Total intangibles	10,383	10,652
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	22	23
Net interest income	22	23
Non-interest income	4,194	3,593
Non-interest expense	3,301	4,170
Intangible amortization	143	100
Income tax expense (benefit)	275	(226)
Net income (loss)	497	(428)
Total assets	21,680	18,464
Total intangibles	12,779	10,021
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	9,785	9,593
Interest expense	941	860
Net interest income	8,844	8,733
Provision for credit losses	1,526	1,574
Non-interest income	716	676
Non-interest expense	5,204	4,808
Income tax expense (benefit)	1,112	1,149
Net income (loss)	1,718	1,878
Total assets	188,547	182,662
Total intangibles	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	1,969	1,635
Interest expense	1,865	647
Net interest income	104	988
Provision for credit losses	325	235
Non-interest income	1,085	(1,775)
Non-interest expense	357	(10)
Income tax expense (benefit)	(259)	(543)
Net income (loss)	766	(469)
Total assets	$ (58,058)	$ (44,254)