Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income, net of taxes	Retained Earnings	Treasury Stock	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2020		75,798
Beginning balance at Dec. 31, 2020	$ 480,461	$ 758	$ 282,206	$ 5,563	$ 200,893	$ (8,959)
Comprehensive income:
Net income	24,653				24,653
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(1,271)			(1,271)
Total comprehensive income	23,382
Exercise of stock options and other share-based compensation, net of shares tendered for payment (in shares)		156
Exercise of stock options and other share-based compensation, net of shares tendered for payment	1,475	$ 2	1,473
Payment of statutory withholding on issuance of restricted stock units	(1,501)		(1,501)
Share-based compensation expense	2,104		2,104
Treasury shares issued for Deferred Compensation Plan funding and redemptions	509		545			(36)
Shares issued pursuant to Employee Stock Plan	2,052		1,554			498
Dividends paid and accrued	(15,526)				(15,526)
Shares issued pursuant to Dividend Reinvestment Plan	23		18			5
Other (in shares)		4
Other	123		123
Ending balance (in shares) at Mar. 31, 2021		75,958
Ending balance at Mar. 31, 2021	493,102	$ 760	286,522	4,292	210,020	(8,492)
Beginning balance (in shares) at Dec. 31, 2020		75,798
Beginning balance at Dec. 31, 2020	480,461	$ 758	282,206	5,563	200,893	(8,959)
Comprehensive income:
Net income	34,218
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(568)
Total comprehensive income	33,650
Ending balance (in shares) at Jun. 30, 2021		75,969
Ending balance at Jun. 30, 2021	488,304	$ 760	289,138	4,995	203,793	(10,382)
Beginning balance (in shares) at Mar. 31, 2021		75,958
Beginning balance at Mar. 31, 2021	493,102	$ 760	286,522	4,292	210,020	(8,492)
Comprehensive income:
Net income	9,565				9,565
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	703			703
Total comprehensive income	10,268
Exercise of stock options and other share-based compensation, net of shares tendered for payment (in shares)		11
Exercise of stock options and other share-based compensation, net of shares tendered for payment	380		380
Share-based compensation expense	2,159		2,159
Purchases of Treasury Stock	(1,835)					(1,835)
Treasury shares issued for Deferred Compensation Plan funding and redemptions	(1)		60			(61)
Dividends paid and accrued	(15,792)				(15,792)
Shares issued pursuant to Dividend Reinvestment Plan	23		17			6
Ending balance (in shares) at Jun. 30, 2021		75,969
Ending balance at Jun. 30, 2021	$ 488,304	$ 760	289,138	4,995	203,793	(10,382)
Beginning balance (in shares) at Dec. 31, 2021	73,769	76,009
Beginning balance at Dec. 31, 2021	$ 452,677	$ 760	294,124	4,000	183,957	(30,164)
Comprehensive income:
Net income	11,329				11,329
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(5,269)			(5,269)
Total comprehensive income	6,060
Exercise of stock options and other share-based compensation, net of shares tendered for payment (in shares)		145
Exercise of stock options and other share-based compensation, net of shares tendered for payment	410	$ 2	408
Payment of statutory withholding on issuance of restricted stock units	(1,069)		(1,069)
Share-based compensation expense	2,298		2,298
Treasury shares issued for Deferred Compensation Plan funding and redemptions	524		110			414
Shares issued pursuant to Employee Stock Plan	1,512		368				$ 1,144
Dividends paid and accrued	(15,859)				(15,859)
Shares issued pursuant to Dividend Reinvestment Plan	25		6			19
Other (in shares)		4
Other	59		59
Ending balance (in shares) at Mar. 31, 2022		76,158
Ending balance at Mar. 31, 2022	$ 446,637	$ 762	296,304	(1,269)	179,427	(28,587)
Beginning balance (in shares) at Dec. 31, 2021	73,769	76,009
Beginning balance at Dec. 31, 2021	$ 452,677	$ 760	294,124	4,000	183,957	(30,164)
Comprehensive income:
Net income	18,149
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(7,214)
Total comprehensive income	$ 10,935
Ending balance (in shares) at Jun. 30, 2022	74,054	76,160
Ending balance at Jun. 30, 2022	$ 437,845	$ 762	298,405	(3,214)	170,267	(28,375)
Beginning balance (in shares) at Mar. 31, 2022		76,158
Beginning balance at Mar. 31, 2022	446,637	$ 762	296,304	(1,269)	179,427	(28,587)
Comprehensive income:
Net income	6,820				6,820
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(1,945)			(1,945)
Total comprehensive income	4,875
Exercise of stock options and other share-based compensation, net of shares tendered for payment (in shares)		2
Share-based compensation expense	2,292		2,292
Treasury shares issued for Deferred Compensation Plan funding and redemptions	(5)		(196)			191
Dividends paid and accrued	(15,980)				(15,980)
Shares issued pursuant to Dividend Reinvestment Plan	$ 26		5			21
Ending balance (in shares) at Jun. 30, 2022	74,054	76,160
Ending balance at Jun. 30, 2022	$ 437,845	$ 762	$ 298,405	$ (3,214)	$ 170,267	$ (28,375)