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
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, 2021		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)