Acquisitions and Asset Purchase - Additional Information (Detail) - USD ($)				12 Months Ended
	Aug. 03, 2015	Jul. 31, 2015	Apr. 08, 2015	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Fair value of purchased credit impaired loans				$ 27,371,000	$ 28,601,000
Contractual amounts				38,379,000	35,030,000
Business acquisition, cash purchase price					1,931,000
Goodwill resulting from acquisition				139,971,000	139,971,000
Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Contractual amounts				$ 1,865,000	$ 2,936,000
FBC Bancshares, Inc. and First Bank, N.A. [Member]
Business Acquisition [Line Items]
Business acquisition, agreement date				Apr. 01, 2015
Payment for all outstanding shares of acquired entity by shares		1,755,374
Subordinated debt, paid off	$ 13,125,000
Fair value of total loans				$ 248,380,000
Total loans of contractual amounts				252,458,000
Goodwill resulting from acquisition				43,922,000
FBC Bancshares, Inc. and First Bank, N.A. [Member] | Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Fair value of purchased credit impaired loans				1,398,000
Contractual amounts				$ 1,704,000
4Trust Mortgage, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, agreement date				Apr. 08, 2015
Business acquisition, cash purchase price			$ 1,900,000
Goodwill resulting from acquisition				$ 1,750,000