Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2015	$ 54,551	$ 72	$ 6,964	$ (31)	$ 47,546
Beginning Balance, shares at Dec. 31, 2015		7,203
Common stock issued on exercise of options and vesting of restricted stock units	72		72
Common stock issued on exercise of options and vesting of restricted stock units, shares		52
Common stock repurchased on vesting of restricted stock units	(433)		(433)
Common stock repurchased on vesting of restricted stock units, shares		(11)
Share-based compensation expense	2,782		2,782
Excess tax benefits from share-based compensation	253		253
Cash dividends on common stock	(6,359)				(6,359)
Unrealized gain (loss) on investments, net of tax	28			28
Net income	18,799				18,799
Ending Balance at Dec. 31, 2016	69,693	$ 72	9,638	(3)	59,986
Ending Balance, shares at Dec. 31, 2016		7,244
Common stock issued on exercise of options and vesting of restricted stock units	163	$ 1	162
Common stock issued on exercise of options and vesting of restricted stock units, shares		86
Common stock repurchased on vesting of restricted stock units	(1,673)		(1,673)
Common stock repurchased on vesting of restricted stock units, shares		(29)
Share-based compensation expense	4,184		4,184
Cash dividends on common stock	(7,276)				(7,276)
Unrealized gain (loss) on investments, net of tax	(1,427)			(1,427)
Net income	25,170				25,170
Ending Balance at Dec. 31, 2017	88,834	$ 73	12,311	(1,430)	77,880
Ending Balance, shares at Dec. 31, 2017		7,301
Common stock issued on exercise of options and vesting of restricted stock units	577	$ 1	576
Common stock issued on exercise of options and vesting of restricted stock units, shares		126
Common stock repurchased on vesting of restricted stock units	(2,952)		(2,952)
Common stock repurchased on vesting of restricted stock units, shares		(32)
Share-based compensation expense	5,502		5,502
Cash dividends on common stock	(7,348)				(7,348)
Unrealized gain (loss) on investments, net of tax	(3,638)			(3,638)
Net income	38,062				38,062
Ending Balance at Dec. 31, 2018	$ 119,037	$ 74	$ 15,437	$ (5,068)	$ 108,594
Ending Balance, shares at Dec. 31, 2018		7,395