Income Taxes - Summary of Net Deferred Tax Asset Reported in Other Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provision for loan losses	$ 13,123	$ 18,748
Unrealized net losses on securities	739
Write-downs of other real estate owned	473	769
Deferred compensation	2,113	3,197
Stock-based compensation	1,351	2,441
Investments in partnership interests	3,758	4,603
Other	275	666
Gross deferred tax assets	21,832	30,424
Unrealized net gains on securities		(59)
Premium on securities of banks acquired	(219)	(453)
Intangibles	(3,359)	(5,365)
Basis difference related to tax credits	(2,713)	(3,435)
Depreciation	(4,563)	(6,758)
Leveraged lease	(821)	(1,408)
Prepaid expense deducted	(887)
Other	(180)	(271)
Gross deferred tax liabilities	(12,742)	(17,749)
Net deferred tax asset	$ 9,090	$ 12,675