Consolidated Statement of Changes in Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total
BALANCE-beginning of period at Dec. 31, 2015	$ 368	$ 378,518	$ 50,099	$ 417		$ 429,402
BALANCE-beginning of period (in shares) at Dec. 31, 2015	36,788
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			5,470			5,470
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				631		631
Issuance of common stock in connection with initial public offering, net of expenses		71				71
Purchase of treasury stock					$ (1,253)	(1,253)
Stock-based compensation expense		620				620
BALANCE-end of period at Jun. 30, 2016	$ 368	379,209	55,569	1,048	(1,253)	434,941
BALANCE-end of period (in shares) at Jun. 30, 2016	36,788
BALANCE-beginning of period at Dec. 31, 2016	$ 372	382,961	49,127	(725)	(1,253)	430,482
BALANCE-beginning of period (in shares) at Dec. 31, 2016	36,988
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income			20,110			20,110
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				(9)		(9)
Issuance of common stock in connection with the exercise of stock options		456				456
Issuance of common stock in connection with the exercise of stock options (in shares)	225
Stock-based compensation expense		702				702
BALANCE-end of period at Jun. 30, 2017	$ 372	$ 384,119	$ 69,237	$ (734)	$ (1,253)	$ 451,741
BALANCE-end of period (in shares) at Jun. 30, 2017	37,213