Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss), net of Taxes	Retained Earnings	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2020		75,798
Beginning balance at Dec. 31, 2020	$ 470,276	$ 758	$ 282,206	$ 5,563	$ 190,708	$ (8,959)
Comprehensive income:
Net income for the period	48,543				48,543
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(1,563)			(1,563)
Total comprehensive income	46,980
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)		207
Exercise of stock options and other share-based compensation, net of shares tendered for payment	2,425	$ 2	2,423
Payment of statutory withholding on issuance of restricted stock units	(1,410)		(1,410)
Share-based compensation expense	8,600		8,600
Purchases of treasury stock	(21,535)					(21,535)
Treasury shares issued for Deferred Compensation Plan funding, net	368		574			(206)
Shares issued pursuant to Employee Stock Plan	2,052		1,554			498
Dividends paid and accrued	(62,800)				(62,800)
Shares issued pursuant to Dividend Reinvestment Plan	92		54			38
Other (in shares)		4
Other	123		123
Ending balance (in shares) at Dec. 31, 2021		76,009
Ending balance at Dec. 31, 2021	445,171	$ 760	294,124	4,000	176,451	(30,164)
Comprehensive income:
Net income for the period	34,243				34,243
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	(7,477)			(7,477)
Total comprehensive income	26,766
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)		148
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	(1,071)		(1,071)
Share-based compensation expense	9,044		9,044
Purchases of treasury stock	0
Treasury shares issued for Deferred Compensation Plan funding, net	374		(634)			1,008
Shares issued pursuant to Employee Stock Plan	1,512		368			1,144
Dividends paid and accrued	(64,092)				(64,092)
Shares issued pursuant to Dividend Reinvestment Plan	106		6			100
Other (in shares)		4
Other	$ 59		59
Ending balance (in shares) at Dec. 31, 2022	74,088	76,161
Ending balance at Dec. 31, 2022	$ 418,279	$ 762	302,304	(3,477)	146,602	(27,912)
Comprehensive income:
Net income for the period	38,386				38,386
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes	1,633			1,633
Total comprehensive income	40,019
Exercise of stock options and other stock-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	8,836		8,836
Purchases of treasury stock	(11,283)					(11,283)
Treasury shares issued for Deferred Compensation Plan funding, net	470		298			172
Shares issued pursuant to Employee Stock Plan	1,135		(139)			1,274
Other (in shares)		1
Other	$ 30		8		22
Ending balance (in shares) at Dec. 31, 2023	73,341	76,329
Ending balance at Dec. 31, 2023	$ 456,616	$ 763	$ 310,436	$ (1,844)	$ 185,010	$ (37,749)