Investment Securities - Summary of Securities Available for Sale in an Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	$ 697,366	$ 612,613
Less than 12 months, Unrealized Losses	5,655	11,420
12 months or longer, Fair Value	136,159	36,982
12 months or longer, Unrealized Losses	10,814	17,917
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	27,053	24,101
Less than 12 months, Unrealized Losses	128	159
12 months or longer, Fair Value	19,932	0
12 months or longer, Unrealized Losses	94	0
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	83,310	116,300
Less than 12 months, Unrealized Losses	896	4,902
12 months or longer, Fair Value	38,004	0
12 months or longer, Unrealized Losses	1,626	0
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	351,936	309,376
Less than 12 months, Unrealized Losses	3,410	5,111
12 months or longer, Fair Value	31,690	0
12 months or longer, Unrealized Losses	712	0
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	0	218
12 months or longer, Unrealized Losses	0	12
Commercial Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	228,307	162,479
Less than 12 months, Unrealized Losses	1,218	1,242
12 months or longer, Fair Value	12,272	0
12 months or longer, Unrealized Losses	186	0
Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	6,760	0
Less than 12 months, Unrealized Losses	3	0
12 months or longer, Fair Value	0	0
12 months or longer, Unrealized Losses	0	0
Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	29,544	28,579
12 months or longer, Unrealized Losses	6,844	15,735
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	4,365	8,185
12 months or longer, Unrealized Losses	1,341	2,170
Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	357
Less than 12 months, Unrealized Losses	0	6
12 months or longer, Fair Value	352	0
12 months or longer, Unrealized Losses	$ 11	$ 0