Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2018	$ 571,535	$ 103,801	$ 467,783	$ (49)
Balance, Shares at Dec. 31, 2018		24,182,000
Net income	18,449		18,449
Share-based compensation	1,392	$ 1,392
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		40,000
Taxes paid related to net share settlement of stock awards	(1,555)	$ (1,555)
Dividends accrued of $0.42, $0.42, $0.375 and $0.375 per share for three months ended March 31, 2020, June 30, 2020 and three months ended March 31,2019, June 30, 2019	(9,151)		(9,151)
Other comprehensive gain (loss)	(27)			(27)
Balance at Mar. 31, 2019	580,643	$ 103,638	477,081	(76)
Balance, Shares at Mar. 31, 2019		24,222,000
Balance at Dec. 31, 2018	571,535	$ 103,801	467,783	(49)
Balance, Shares at Dec. 31, 2018		24,182,000
Net income	37,937
Balance at Jun. 30, 2019	592,309	$ 104,984	487,407	(82)
Balance, Shares at Jun. 30, 2019		24,253,000
Balance at Mar. 31, 2019	580,643	$ 103,638	477,081	(76)
Balance, Shares at Mar. 31, 2019		24,222,000
Net income	19,488		19,488
Share-based compensation	1,354	$ 1,354
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		31,000
Taxes paid related to net share settlement of stock awards	(8)	$ (8)
Dividends accrued of $0.42, $0.42, $0.375 and $0.375 per share for three months ended March 31, 2020, June 30, 2020 and three months ended March 31,2019, June 30, 2019	(9,162)		(9,162)
Other comprehensive gain (loss)	(6)			(6)
Balance at Jun. 30, 2019	592,309	$ 104,984	487,407	(82)
Balance, Shares at Jun. 30, 2019		24,253,000
Balance at Dec. 31, 2019	$ 634,036	$ 106,360	527,746	(70)
Balance, Shares at Dec. 31, 2019	24,296,000	24,296,000
Net income	$ 20,159		20,159
Share-based compensation	1,723	$ 1,723
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		50,000
Repurchased common stock	(7,852)	$ (725)	(7,127)
Repurchased common stock, Shares		(164,000)
Taxes paid related to net share settlement of stock awards	(401)	$ (401)
Dividends accrued of $0.42, $0.42, $0.375 and $0.375 per share for three months ended March 31, 2020, June 30, 2020 and three months ended March 31,2019, June 30, 2019	(10,219)		(10,219)
Other comprehensive gain (loss)	158			158
Balance at Mar. 31, 2020	637,604	$ 106,957	530,559	88
Balance, Shares at Mar. 31, 2020		24,182,000
Balance at Dec. 31, 2019	$ 634,036	$ 106,360	527,746	(70)
Balance, Shares at Dec. 31, 2019	24,296,000	24,296,000
Net income	$ 42,708
Balance at Jun. 30, 2020	$ 643,836	$ 106,010	537,775	51
Balance, Shares at Jun. 30, 2020	24,085,000	24,085,000
Balance at Mar. 31, 2020	$ 637,604	$ 106,957	530,559	88
Balance, Shares at Mar. 31, 2020		24,182,000
Net income	22,549		22,549
Share-based compensation	1,501	$ 1,501
Common stock issued under stock Plans, net of shares withheld for employee taxes, Shares		19,000
Repurchased common stock	(5,648)	$ (509)	(5,139)
Repurchased common stock, Shares		(116,000)
Taxes paid related to net share settlement of stock awards	(1,939)	$ (1,939)
Dividends accrued of $0.42, $0.42, $0.375 and $0.375 per share for three months ended March 31, 2020, June 30, 2020 and three months ended March 31,2019, June 30, 2019	(10,194)		(10,194)
Other comprehensive gain (loss)	(37)			(37)
Balance at Jun. 30, 2020	$ 643,836	$ 106,010	$ 537,775	$ 51
Balance, Shares at Jun. 30, 2020	24,085,000	24,085,000