Consolidated Statement of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
BALANCE-beginning of period at Dec. 31, 2013	$ 208	$ 179,219	$ 19,918	$ (127)	$ 199,218
BALANCE-beginning of period (in shares) at Dec. 31, 2013	20,771
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			12,695		12,695
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				1,150	1,150
Issuance of common stock in connection with initial public offering, net of expenses	$ 54	72,488			72,542
Issuance of common stock in connection with initial public offering, net of expenses (in shares)	5,391
Issuance of common stock in connection with the exercise of stock options		76			76
Issuance of common stock in connection with the exercise of stock options (in shares)	9
Stock-based compensation expense		283			283
BALANCE-end of period at Sep. 30, 2014	$ 262	252,066	32,613	1,023	285,964
BALANCE-end of period (in shares) at Sep. 30, 2014	26,171
BALANCE-beginning of period at Dec. 31, 2014	$ 262	252,421	34,660	1,062	288,405
BALANCE-beginning of period (in shares) at Dec. 31, 2014	26,176
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			12,866		12,866
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				308	308
Issuance of common stock in connection with the exercise of stock options	$ 1	954			955
Issuance of common stock in connection with the exercise of stock options (in shares)	101
Stock-based compensation expense		695			695
BALANCE-end of period at Sep. 30, 2015	$ 263	$ 254,070	$ 47,526	$ 1,370	$ 303,229
BALANCE-end of period (in shares) at Sep. 30, 2015	26,277