Income Taxes - Schedule of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income before provision for income taxes									$ 31,205	$ 30,531	$ 24,943
Applicable statutory Federal income tax rate									35.00%	35.00%	35.00%
Computed "expected" Federal income tax expense									$ 10,922	$ 10,686	$ 8,730
Increase (decrease) in Federal income tax expense resulting from:
Tax exempt interest									(291)	(109)	(61)
ESOP fair market value adjustment									111	99	87
ESOP dividends									(234)	(229)	(233)
Earnings on BOLI									(525)	(517)	(491)
Merger related expenses									132
State income taxes net of Federal benefit									751	695	642
Other items, net									17	(14)	(61)
Income tax expense (benefit)	$ 2,777	$ 2,582	$ 2,779	$ 2,745	$ 2,491	$ 2,790	$ 2,767	$ 2,563	$ 10,883	$ 10,611	$ 8,613