Earnings Per Share - Components of Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, 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
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 13,178	$ 11,662	$ 10,233	$ 8,136	$ 9,010	$ 8,268	$ 8,226	$ 7,190	$ 43,214	$ 32,694	$ 23,818
Weighted-average number of common shares outstanding – basic									26,719,626	24,485,078	14,758,036
Share-based compensation plans									968,671	464,054	275,771
Warrants									250,707	198,520	131,976
Weighted-average number of common shares – diluted									27,939,004	25,147,652	15,165,783
Basic earnings per share	$ 0.49	$ 0.44	$ 0.38	$ 0.31	$ 0.33	$ 0.30	$ 0.35	$ 0.35	$ 1.62	$ 1.34	$ 1.61
Diluted earnings per share	$ 0.47	$ 0.42	$ 0.37	$ 0.29	$ 0.32	$ 0.30	$ 0.34	$ 0.35	$ 1.55	$ 1.30	$ 1.57