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 (loss)			(3,516)			(3,516)
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				562		562
Issuance of common stock in connection with the exercise of stock options	$ 1	71				72
Issuance of common stock in connection with the exercise of stock options (in shares)	251
Purchase of treasury stock					$ (1,253)	(1,253)
Purchase of treasury stock (in shares)	(178)
Stock-based compensation expense		948				948
BALANCE-end of period at Sep. 30, 2016	$ 369	379,537	46,583	979	(1,253)	426,215
BALANCE-end of period (in shares) at Sep. 30, 2016	36,861
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 (loss)			31,517			31,517
Net change in unrealized gains and losses on available-for-sale securities, net of taxes and reclassification adjustment				(1,216)		(1,216)
Issuance of common stock in connection with the exercise of stock options	$ 1	469				470
Issuance of common stock in connection with the exercise of stock options (in shares)	286
Stock-based compensation expense		1,058				1,058
BALANCE-end of period at Sep. 30, 2017	$ 373	$ 384,488	$ 80,644	$ (1,941)	$ (1,253)	$ 462,311
BALANCE-end of period (in shares) at Sep. 30, 2017	37,274