Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2020	$ 198,235,000	$ 76,000	$ 24,885,000	$ 7,564,000	$ 165,710,000
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	815,000		815,000
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	(107,000)		(107,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(1)
Share-based compensation expense	1,060,000		1,060,000
Company repurchase of common stock	(3,436,000)		(170,000)		(3,266,000)
Company repurchase of common stock, shares		(49)
Cash dividends on common stock	(2,278,000)				(2,278,000)
Unrealized gain (loss) on investments, net of tax	(5,250,000)			(5,250,000)
Net income (loss)	(4,554,000)				(4,554,000)
Ending Balance at Mar. 31, 2021	184,485,000	$ 76,000	26,483,000	2,314,000	155,612,000
Ending Balance, shares at Mar. 31, 2021		7,554
Beginning Balance at Dec. 31, 2020	198,235,000	$ 76,000	24,885,000	7,564,000	165,710,000
Beginning Balance, shares at Dec. 31, 2020		7,566
Unrealized gain (loss) on investments, net of tax	(4,100,000)
Net income (loss)	27,465,000
Ending Balance at Sep. 30, 2021	207,633,000	$ 75,000	27,981,000	3,464,000	176,113,000
Ending Balance, shares at Sep. 30, 2021		7,505
Beginning Balance at Mar. 31, 2021	184,485,000	$ 76,000	26,483,000	2,314,000	155,612,000
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	61,000		61,000
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	(287,000)		(287,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(4)
Share-based compensation expense	1,335,000		1,335,000
Company repurchase of common stock	(3,142,000)	$ (1,000)	(155,000)		(2,986,000)
Company repurchase of common stock, shares		(42)
Cash dividends on common stock	(2,271,000)				(2,271,000)
Unrealized gain (loss) on investments, net of tax	2,151,000			2,151,000
Net income (loss)	17,090,000				17,090,000
Ending Balance at Jun. 30, 2021	199,422,000	$ 75,000	27,437,000	4,465,000	167,445,000
Ending Balance, shares at Jun. 30, 2021		7,523
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	280,000.00	$ 1,000	279,000
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		51
Common stock repurchased on vesting of restricted stock units and performance awards	(1,010,000)		(1,010,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(14)
Share-based compensation expense	1,479,000		1,479,000
Company repurchase of common stock	(4,197,000)	$ (1,000)	(204,000)		(3,992,000)
Company repurchase of common stock, shares		(55)
Cash dividends on common stock	(2,269,000)				(2,269,000)
Unrealized gain (loss) on investments, net of tax	(1,001,000)			(1,001,000)
Net income (loss)	14,929,000				14,929,000
Ending Balance at Sep. 30, 2021	207,633,000	$ 75,000	27,981,000	3,464,000	176,113,000
Ending Balance, shares at Sep. 30, 2021		7,505
Beginning Balance at Dec. 31, 2021	208,530,000	$ 74,000	29,054,000	1,079,000	178,323,000
Beginning Balance, shares at Dec. 31, 2021		7,415
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	411,000		411,000
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		18
Common stock repurchased on vesting of restricted stock units and performance awards	(185,000)		(185,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(4)
Share-based compensation expense	1,830,000		1,830,000
Company repurchase of common stock	(8,575,000)	$ (1,000)	(484,000)		(8,090,000)
Company repurchase of common stock, shares		(115)
Cash dividends on common stock	(2,229,000)				(2,229,000)
Unrealized gain (loss) on investments, net of tax	(14,358,000)			(14,358,000)
Net income (loss)	288,000				288,000
Ending Balance at Mar. 31, 2022	185,712,000	$ 73,000	30,626,000	(13,279,000)	168,292,000
Ending Balance, shares at Mar. 31, 2022		7,314
Beginning Balance at Dec. 31, 2021	208,530,000	$ 74,000	29,054,000	1,079,000	178,323,000
Beginning Balance, shares at Dec. 31, 2021		7,415
Unrealized gain (loss) on investments, net of tax	(31,882,000)
Net income (loss)	35,740,000
Ending Balance at Sep. 30, 2022	171,363,000	$ 70,000	31,351,000	(30,803,000)	170,745,000
Ending Balance, shares at Sep. 30, 2022		6,962
Beginning Balance at Mar. 31, 2022	185,712,000	$ 73,000	30,626,000	(13,279,000)	168,292,000
Beginning Balance, shares at Mar. 31, 2022		7,314
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		12
Common stock repurchased on vesting of restricted stock units and performance awards	(258,000)		(258,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(3)
Share-based compensation expense	1,766,000		1,766,000
Company repurchase of common stock	(19,917,000)	$ (2,000)	(1,193,000)		(18,722,000)
Company repurchase of common stock, shares		(270)
Cash dividends on common stock	(2,195,000)				(2,195,000)
Unrealized gain (loss) on investments, net of tax	(8,624,000)			(8,624,000)
Net income (loss)	18,014,000				18,014,000
Ending Balance at Jun. 30, 2022	174,498,000	$ 71,000	30,941,000	(21,903,000)	165,389,000
Ending Balance, shares at Jun. 30, 2022		7,053
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards	300,000	$ 1,000	299,000
Common stock issued on exercise of options, purchase of ESPP shares and vesting of restricted stock units and performance awards, shares		54
Common stock repurchased on vesting of restricted stock units and performance awards	(1,178,000)		(1,178,000)
Common stock repurchased on vesting of restricted stock units and performance awards, shares		(16)
Share-based compensation expense	1,893,000		1,893,000
Company repurchase of common stock	(10,560,000)	$ (2,000)	(604,000)		(9,954,000)
Company repurchase of common stock, shares		(129)
Cash dividends on common stock	(2,128,000)				(2,128,000)
Unrealized gain (loss) on investments, net of tax	(8,900,000)			(8,900,000)
Net income (loss)	17,438,000				17,438,000
Ending Balance at Sep. 30, 2022	$ 171,363,000	$ 70,000	$ 31,351,000	$ (30,803,000)	$ 170,745,000
Ending Balance, shares at Sep. 30, 2022		6,962