Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2019	$ 171,799	$ 75	$ 20,227	$ 2,819	$ 148,678
Beginning Balance, shares at Dec. 31, 2019		7,514
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	904	$ 1	903
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		56
Common stock repurchased on vesting of restricted stock units and performance awards	(378)		(378)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(6)
Share-based compensation expense	342		342
Company repurchase of common stock	(2,987)	$ (1)	(169)		(2,817)
Company repurchase of common stock, shares		(59)
Cash dividends on common stock	(2,262)				(2,262)
Unrealized gain (loss) on investments, net of tax	(2,735)			(2,735)
Net (loss) income	(3,407)				(3,407)
Ending Balance at Mar. 31, 2020	161,276	$ 75	20,925	84	140,192
Ending Balance, shares at Mar. 31, 2020		7,505
Beginning Balance at Dec. 31, 2019	171,799	$ 75	20,227	2,819	148,678
Beginning Balance, shares at Dec. 31, 2019		7,514
Unrealized gain (loss) on investments, net of tax	4,142
Net (loss) income	8,103
Ending Balance at Jun. 30, 2020	179,888	$ 76	23,421	6,961	149,430
Ending Balance, shares at Jun. 30, 2020		7,598
Beginning Balance at Mar. 31, 2020	161,276	$ 75	20,925	84	140,192
Beginning Balance, shares at Mar. 31, 2020		7,505
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	1,810	$ 1	1,809
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		96
Common stock repurchased on vesting of restricted stock units and performance awards	(110)		(110)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(3)
Share-based compensation expense	797		797
Cash dividends on common stock	(2,272)				(2,272)
Unrealized gain (loss) on investments, net of tax	6,877			6,877
Net (loss) income	11,510				11,510
Ending Balance at Jun. 30, 2020	179,888	$ 76	23,421	6,961	149,430
Ending Balance, shares at Jun. 30, 2020		7,598
Beginning Balance at Dec. 31, 2020	198,235	$ 76	24,885	7,564	165,710
Beginning Balance, shares at Dec. 31, 2020		7,566
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	815		815
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		38
Common stock repurchased on vesting of restricted stock units and performance awards	(107)		(107)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(1)
Share-based compensation expense	1,060		1,060
Company repurchase of common stock	(3,436)		(170)		(3,266)
Company repurchase of common stock, shares		(49)
Cash dividends on common stock	(2,278)				(2,278)
Unrealized gain (loss) on investments, net of tax	(5,250)			(5,250)
Net (loss) income	(4,554)				(4,554)
Ending Balance at Mar. 31, 2021	184,485	$ 76	26,483	2,314	155,612
Ending Balance, shares at Mar. 31, 2021		7,554
Beginning Balance at Dec. 31, 2020	198,235	$ 76	24,885	7,564	165,710
Beginning Balance, shares at Dec. 31, 2020		7,566
Unrealized gain (loss) on investments, net of tax	(3,099)
Net (loss) income	12,536
Ending Balance at Jun. 30, 2021	199,422	$ 75	27,437	4,465	167,445
Ending Balance, shares at Jun. 30, 2021		7,523
Beginning Balance at Mar. 31, 2021	184,485	$ 76	26,483	2,314	155,612
Beginning Balance, shares at Mar. 31, 2021		7,554
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	61		61
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		15
Common stock repurchased on vesting of restricted stock units and performance awards	(287)		(287)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(4)
Share-based compensation expense	1,335		1,335
Company repurchase of common stock	(3,142)	$ (1)	(155)		(2,986)
Company repurchase of common stock, shares		(42)
Cash dividends on common stock	(2,271)				(2,271)
Unrealized gain (loss) on investments, net of tax	2,151			2,151
Net (loss) income	17,090				17,090
Ending Balance at Jun. 30, 2021	$ 199,422	$ 75	$ 27,437	$ 4,465	$ 167,445
Ending Balance, shares at Jun. 30, 2021		7,523