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, 2016	$ 69,693	$ 72	$ 9,638	$ (3)	$ 59,986
Beginning 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/stock awards	(1,673)		(1,673)
Common stock repurchased on vesting of restricted stock units/stock awards, 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/stock awards	(2,952)		(2,952)
Common stock repurchased on vesting of restricted stock units/stock awards, 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
Common stock issued on exercise of options and vesting of restricted stock units	754	$ 1	753
Common stock issued on exercise of options and vesting of restricted stock units, shares		157
Common stock repurchased on vesting of restricted stock units/stock awards	(3,136)		(3,136)
Common stock repurchased on vesting of restricted stock units/stock awards, shares		(38)
Share-based compensation expense	7,173		7,173
Cash dividends on common stock	(8,208)				(8,208)
Unrealized gain (loss) on investments, net of tax	7,887			7,887
Net income	48,292				48,292
Ending Balance at Dec. 31, 2019	$ 171,799	$ 75	$ 20,227	$ 2,819	$ 148,678
Ending Balance, shares at Dec. 31, 2019		7,514