Consolidated Statement of Changes in Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock	Capital Surplus	Retained Earnings (Deficit)	Accumulated Other Comprehensive Income (Loss)	Total
BALANCE-beginning of period at Dec. 31, 2011	$ 180	$ 153,664	$ (1,227)	$ 806	$ 153,423
BALANCE-beginning of period (in shares) at Dec. 31, 2011	17,970
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			8,535		8,535
Net change in unrealized gains and losses on available-for-sale securities, net of taxes of $641, $1,099 and $615, respectively, and reclassification adjustment				1,195	1,195
Issuance of common stock in connection with initial public offering, net of expenses	27	24,707			24,734
Issuance of common stock in connection with initial public offering, net of expenses (in shares)	2,778
Stockbased compensation expense		324			324
BALANCE-end of period at Dec. 31, 2012	207	178,695	7,308	2,001	188,211
BALANCE-end of period (in shares) at Dec. 31, 2012	20,748
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			12,610		12,610
Net change in unrealized gains and losses on available-for-sale securities, net of taxes of $641, $1,099 and $615, respectively, and reclassification adjustment				(2,128)	(2,128)
Issuance of common stock in connection with the exercise of stock options	1	189			190
Issuance of common stock in connection with the exercise of stock options (in shares)	23
Stockbased compensation expense		335			335
BALANCE-end of period at Dec. 31, 2013	208	179,219	19,918	(127)	199,218
BALANCE-end of period (in shares) at Dec. 31, 2013	20,771
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			14,742		14,742
Net change in unrealized gains and losses on available-for-sale securities, net of taxes of $641, $1,099 and $615, respectively, and reclassification adjustment				1,189	1,189
Issuance of common stock in connection with initial public offering, net of expenses	54	72,537			72,591
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		117			117
Issuance of common stock in connection with the exercise of stock options (in shares)	14
Stockbased compensation expense		548			548
BALANCE-end of period at Dec. 31, 2014	$ 262	$ 252,421	$ 34,660	$ 1,062	$ 288,405
BALANCE-end of period (in shares) at Dec. 31, 2014	26,176