Income Taxes - Schedule of Income (Loss) Before Income Tax Expense (Benefit) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal income tax at statutory rate, amount									$ 22,185	$ 17,604	$ 12,631
Federal income tax at statutory rate, percentage of pretax income	35.00%								35.00%	35.00%	35.00%
State income tax, amount									1,355	353	184
State income tax, percentage of pretax income									2.14%	0.70%	0.51%
Tax-exempt interest, amount									(260)	(155)	(85)
Tax-exempt interest, percentage of pretax income									(0.41%)	(0.31%)	(0.24%)
Interest disallowance, amount									11	7	4
Interest disallowance, percentage of pretax income									0.02%	0.01%	0.01%
Bank-owned life insurance, amount									(1,296)	(868)	(466)
Bank-owned life insurance, percentage of pretax income									(2.04%)	(1.73%)	(1.29%)
Other, amount									(1,821)	663	4
Other, percentage of pretax income									(2.88%)	1.33%	0.01%
Total	$ 7,289	$ 3,940	$ 5,517	$ 3,429	$ 4,810	$ 4,494	$ 4,429	$ 3,871	$ 20,174	$ 17,604	$ 12,272
Effective income tax rate, percentage of pretax income									31.83%	35.00%	34.00%