Consolidated Statement of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2017	$ 315	$ 217,906	$ 381,048	$ (57,675)	$ (8,986)	$ 532,608
Net income	0	0	11,412	0	0	11,412
Award of common shares released from Employee Benefit Trust	0	2,488	0	0	0	2,488
Vesting of restricted stock unit awards	0	(4,731)	(170)	4,901	0	0
Stock-based compensation expense	0	3,452	0	0	0	3,452
Repurchase of shares to satisfy tax obligation	0	0	0	(2,050)	0	(2,050)
Dividends on common stock	0	0	(5,795)	0	0	(5,795)
Other comprehensive income (loss)	0	0	0	0	(895)	(895)
Purchase of treasury shares	0	0	0	(5,913)	0	(5,913)
Reclassification of the Income tax effects of Tax Cuts and Jobs Act from AOCI to Retained Earnings	0	0	2,073	0	(2,073)	0
Impact of adoption of Accounting Standard Update 2016-01	0	0	(775)	0	775	0
Balance at Mar. 31, 2018	315	219,115	387,793	(60,737)	(11,179)	535,307
Balance at Dec. 31, 2017	315	217,906	381,048	(57,675)	(8,986)	532,608
Net income						42,668
Other comprehensive income (loss)					(3,269)	(3,269)
Reclassification of the Income tax effects of Tax Cuts and Jobs Act from AOCI to Retained Earnings			2,073		(2,073)
Impact of adoption of Accounting Standard Update 2016-01					779
Balance at Sep. 30, 2018	315	221,622	407,590	(74,222)	(13,549)	541,756
Balance at Mar. 31, 2018	315	219,115	387,793	(60,737)	(11,179)	535,307
Net income	0	0	13,923	0	0	13,923
Award of common shares released from Employee Benefit Trust	0	90	0	0	0	90
Exercise of stock options	0	(1)	0	7	0	6
Stock-based compensation expense	0	1,228	0	0	0	1,228
Repurchase of shares to satisfy tax obligation	0	0	0	(1)	0	(1)
Dividends on common stock	0	0	(5,752)	0	0	(5,752)
Other comprehensive income (loss)	0	0	0	0	(832)	(832)
Purchase of treasury shares	0	0	0	(5,925)	0	(5,925)
Impact of adoption of Accounting Standard Update 2016-01	0	0	(4)	0	4	0
Balance at Jun. 30, 2018	315	220,432	395,960	(66,656)	(12,007)	538,044
Net income	0	0	17,333	0	0	17,333
Award of common shares released from Employee Benefit Trust	0	74	0	0	0	74
Vesting of restricted stock unit awards	0	(177)	(6)	183	0	0
Stock-based compensation expense	0	1,293	0	0	0	1,293
Repurchase of shares to satisfy tax obligation	0	0	0	(87)	0	(87)
Dividends on common stock	0	0	(5,697)	0	0	(5,697)
Other comprehensive income (loss)	0	0		0	(1,542)	(1,542)
Purchase of treasury shares	0	0	0	(7,662)	0	(7,662)
Balance at Sep. 30, 2018	315	221,622	407,590	(74,222)	(13,549)	541,756
Balance at Dec. 31, 2018	315	222,720	414,327	(75,146)	(12,752)	549,464
Impact of adoption of ASC 842 - Leases | Accounting Standards Update 2016-02 [Member]	0	0	2,716	0	0	2,716
Net income	0	0	7,068	0	0	7,068
Award of common shares released from Employee Benefit Trust	0	2,086	0	0	0	2,086
Vesting of restricted stock unit awards	0	(5,878)	(210)	6,088	0	0
Exercise of stock options	0	0	(3)	6	0	3
Stock-based compensation expense	0	3,931	0	0	0	3,931
Repurchase of shares to satisfy tax obligation	0	0	0	(1,877)	0	(1,877)
Dividends on common stock	0	0	(6,042)	0	0	(6,042)
Other comprehensive income (loss)	0	0	0	0	2,210	2,210
Balance at Mar. 31, 2019	315	222,859	417,856	(70,929)	(10,542)	559,559
Balance at Dec. 31, 2018	315	222,720	414,327	(75,146)	(12,752)	549,464
Net income						28,348
Other comprehensive income (loss)					(217)	(217)
Reclassification of the Income tax effects of Tax Cuts and Jobs Act from AOCI to Retained Earnings			0
Balance at Sep. 30, 2019	315	225,471	427,062	(71,487)	(12,969)	568,392
Balance at Mar. 31, 2019	315	222,859	417,856	(70,929)	(10,542)	559,559
Net income	0	0	10,556	0	0	10,556
Award of common shares released from Employee Benefit Trust	0	81	0	0	0	81
Vesting of restricted stock unit awards	0	(24)	0	24	0	0
Stock-based compensation expense	0	1,315	0	0	0	1,315
Repurchase of shares to satisfy tax obligation	0	0	0	(8)	0	(8)
Dividends on common stock	0	0	(6,039)	0	0	(6,039)
Other comprehensive income (loss)	0	0	0	0	(74)	(74)
Balance at Jun. 30, 2019	315	224,231	422,373	(70,913)	(10,616)	565,390
Net income	0	0	10,724	0	0	10,724
Award of common shares released from Employee Benefit Trust	0	66	0	0	0	66
Vesting of restricted stock unit awards	0	(197)	0	197	0	0
Stock-based compensation expense	0	1,371	0	0	0	1,371
Repurchase of shares to satisfy tax obligation	0	0	0	0	0	0
Dividends on common stock	0	0	(6,035)	0	0	(6,035)
Other comprehensive income (loss)	0	0	0	0	(2,353)	(2,353)
Purchase of treasury shares	0	0	0	(771)	0	(771)
Balance at Sep. 30, 2019	$ 315	$ 225,471	$ 427,062	$ (71,487)	$ (12,969)	$ 568,392