Consolidated Statement of Changes in Shareholders' Equity (unaudited) (USD $) In Thousands, unless otherwise specified	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
BALANCE-beginning of period at Dec. 31, 2012	$ 207	$ 178,695	$ 7,308	$ 2,001	$ 188,211
BALANCE-beginning of period (in shares) at Dec. 31, 2012	20,748
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			9,546		9,546
Net change in unrealized gains and losses on available‑for‑sale securities, net of taxes of $414 and $60, respectively,and reclassification adjustment				(1,636)	(1,636)
Stock‑based compensation expense		252			252
BALANCE-end of period at Sep. 30, 2013	207	178,947	16,854	365	196,373
BALANCE-end of period (in shares) at Sep. 30, 2013	20,748
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 of $414 and $60, respectively,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