Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss, net of taxes	Retained Earnings	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2021		76,009
Beginning balance at Dec. 31, 2021	$ 452,677	$ 760	$ 294,124	$ 4,000	$ 183,957	$ (30,164)
Comprehensive income:
Net income for the period	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, net	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		76,009
Beginning balance at Dec. 31, 2021	452,677	$ 760	294,124	4,000	183,957	(30,164)
Comprehensive income:
Net income for the period	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		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 for the period	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, net	(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		76,160
Ending balance at Jun. 30, 2022	$ 437,845	$ 762	298,405	(3,214)	170,267	(28,375)
Beginning balance (in shares) at Dec. 31, 2022	74,088	76,161
Beginning balance at Dec. 31, 2022	$ 426,172	$ 762	302,304	(3,477)	154,495	(27,912)
Comprehensive income:
Net income for the period	12,684				12,684
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	1,207			1,207
Total comprehensive income	13,891
Exercise of stock options and other share-based compensation, net of shares tendered for payment (in shares)		167
Exercise of stock options and other share-based compensation, net of shares tendered for payment	0	$ 1	(1)
Payment of statutory withholding on issuance of restricted stock units	(870)		(870)
Share-based compensation expense	1,973		1,973
Purchases of treasury stock	(2,223)					(2,223)
Treasury shares issued for Deferred Compensation Plan, net	475		307			168
Shares issued pursuant to Employee Stock Plan	1,135		(139)			1,274
Other (in shares)		1
Other	19		8		11
Ending balance (in shares) at Mar. 31, 2023		76,329
Ending balance at Mar. 31, 2023	$ 440,572	$ 763	303,582	(2,270)	167,190	(28,693)
Beginning balance (in shares) at Dec. 31, 2022	74,088	76,161
Beginning balance at Dec. 31, 2022	$ 426,172	$ 762	302,304	(3,477)	154,495	(27,912)
Comprehensive income:
Net income for the period	21,282
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	347
Total comprehensive income	$ 21,629
Ending balance (in shares) at Jun. 30, 2023	74,195	76,329
Ending balance at Jun. 30, 2023	$ 450,589	$ 763	305,853	(3,130)	175,794	(28,691)
Beginning balance (in shares) at Mar. 31, 2023		76,329
Beginning balance at Mar. 31, 2023	440,572	$ 763	303,582	(2,270)	167,190	(28,693)
Comprehensive income:
Net income for the period	8,598				8,598
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(860)			(860)
Total comprehensive income	7,738
Share-based compensation expense	2,278		2,278
Treasury shares issued for Deferred Compensation Plan, net	(5)		(7)			2
Other	$ 6				6
Ending balance (in shares) at Jun. 30, 2023	74,195	76,329
Ending balance at Jun. 30, 2023	$ 450,589	$ 763	$ 305,853	$ (3,130)	$ 175,794	$ (28,691)