Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	ASU 2017-08 [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] ASU 2017-08 [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Employee Stock Loans [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2018	$ 455,941		$ 173	$ 379,085	$ 101,326		$ (4,867)	$ (121)	$ (19,655)
Beginning balance, shares at Dec. 31, 2018			15,793,095
Net income (loss)	15,565				15,565
Other comprehensive income (loss), net of tax effects	4,444						4,444
Stock-based compensation	2,349			2,349
Stock based compensation, shares			9,104
Common stock issued upon exercise of stock options	316			316
Common stock issued upon exercise of stock options, shares			17,502
Common stock issued under stock-based incentive plan	1		$ 1
Common stock issued under stock-based incentive plan, shares			22,428
Common stock issued under employee stock purchase plan	405			405
Common stock issued under employee stock purchase plan, share			19,221
Repayment on employee stock loans	44							44
Treasury stock purchases	(10,867)								(10,867)
Treasury stock purchases, shares			(421,016)
Cumulative effect of change in accounting principle from implementation of ASU 2017-08		$ (1,148)				$ (1,148)
Ending balance at Sep. 30, 2019	467,050		$ 174	382,155	115,743		(423)	(77)	(30,522)
Ending balance, shares at Sep. 30, 2019			15,440,334
Beginning balance at Jun. 30, 2019	458,406		$ 173	381,133	105,337		(1,291)	(83)	(26,863)
Beginning balance, shares at Jun. 30, 2019			15,563,873
Net income (loss)	10,406				10,406
Other comprehensive income (loss), net of tax effects	868						868
Stock-based compensation	617			617
Common stock issued under stock-based incentive plan	1		$ 1
Common stock issued under stock-based incentive plan, shares			450
Common stock issued under employee stock purchase plan	405			405
Common stock issued under employee stock purchase plan, share			19,221
Repayment on employee stock loans	6							6
Treasury stock purchases	(3,659)								(3,659)
Treasury stock purchases, shares			(143,210)
Ending balance at Sep. 30, 2019	467,050		$ 174	382,155	115,743		(423)	(77)	(30,522)
Ending balance, shares at Sep. 30, 2019			15,440,334
Beginning balance at Dec. 31, 2019	478,060		$ 174	382,731	125,757		(3)	(77)	(30,522)
Beginning balance, shares at Dec. 31, 2019			15,444,434
Net income (loss)	(87,458)				(87,458)
Other comprehensive income (loss), net of tax effects	21,077						21,077
Stock-based compensation	2,670			2,670
Stock based compensation, shares			17,703
Common stock issued upon exercise of stock options	20			20
Common stock issued upon exercise of stock options, shares			1,150
Common stock issued under stock-based incentive plan, shares			34,591
Common stock issued under employee stock purchase plan	596			596
Common stock issued under employee stock purchase plan, share			34,593
Repayment on employee stock loans	34							34
Treasury stock purchases	(12,827)								(12,827)
Treasury stock purchases, shares			(678,984)
Ending balance at Sep. 30, 2020	402,172		$ 174	386,017	38,299		21,074	(43)	(43,349)
Ending balance, shares at Sep. 30, 2020			14,853,487
Beginning balance at Jun. 30, 2020	479,766		$ 174	384,955	128,704		3,390	(43)	(37,414)
Beginning balance, shares at Jun. 30, 2020			15,218,301
Net income (loss)	(90,405)				(90,405)
Other comprehensive income (loss), net of tax effects	17,684						17,684
Stock-based compensation	812			812
Common stock issued upon exercise of stock options	8			8
Common stock issued upon exercise of stock options, shares			500
Common stock issued under stock-based incentive plan, shares			(380)
Common stock issued under employee stock purchase plan	242			242
Common stock issued under employee stock purchase plan, share			17,829
Treasury stock purchases	$ (5,935)								(5,935)
Treasury stock purchases, shares	(383,523)		(383,523)
Ending balance at Sep. 30, 2020	$ 402,172		$ 174	$ 386,017	$ 38,299		$ 21,074	$ (43)	$ (43,349)
Ending balance, shares at Sep. 30, 2020			14,853,487