Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	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			12,610		12,610
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				(2,128)	(2,128)
Issuance of common stock in connection with initial public offering, net of expenses	$ 1	189			190
Issuance of common stock in connection with initial public offering, net of expenses (in shares)	23
Stock-based 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 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
Stock-based 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			15,439		15,439
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				(645)	(645)
Issuance of common stock in connection with initial public offering, net of expenses	$ 105	123,638			123,743
Issuance of common stock in connection with initial public offering, net of expenses (in shares)	10,442
Issuance of common stock in connection with the exercise of stock options	$ 1	1,533			1,534
Issuance of common stock in connection with the exercise of stock options (in shares)	170
Stock-based compensation expense		926			926
BALANCE-end of period at Dec. 31, 2015	$ 368	$ 378,518	$ 50,099	$ 417	$ 429,402
BALANCE-end of period (in shares) at Dec. 31, 2015	36,788