Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance at at Dec. 31, 2017	$ 395,279	$ 591	$ 471,456	$ (13,748)	$ (63,020)
Balance at (in shares) at Dec. 31, 2017		59,057,195
Stock-based compensation plans
Grant of restricted stock	0	$ 1	(1)
Grant of restricted stock (in shares)		101,400
Issuance of common shares, net of withholdings	(1,332)	$ 1	(1,333)
Withholdings of common shares, net of issuances (in shares)		80,092
Forfeited restricted stock	0	$ 0	0
Stock Repurchased and Retired During Period, Shares		(157,000)
Stock Repurchased and Retired During Period, Value	(3,580)	$ (2)	(3,578)
Bond hedge reclassification	(50,435)		(50,435)
Note conversion obligation reclassification	50,999		50,999
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2014-09 [Member]	514			514
Forfeited restricted stock (in shares)		(1,300)
Amortization of stock awards and restricted stock	2,304		2,304
NET EARNINGS	40,512
Total comprehensive income (loss)	41,831			40,512	1,319
Balance at at Jun. 30, 2018	435,580	$ 591	469,412	27,278	(61,701)
Balance at (in shares) at Jun. 30, 2018		59,080,387
Balance at at Mar. 31, 2018	408,498	$ 591	467,570	2,644	(62,307)
Balance at (in shares) at Mar. 31, 2018		59,080,512
Stock-based compensation plans
Issuance of common shares, net of withholdings	(12)	$ 0	(12)
Withholdings of common shares, net of issuances (in shares)		1,175
Bond hedge reclassification	(50,435)		(50,435)
Note conversion obligation reclassification	50,999		50,999
Amortization of stock awards and restricted stock	1,290		1,290
NET EARNINGS	24,634			24,634
Total comprehensive income (loss)	25,240
Other comprehensive income (loss), net of tax					606
Balance at at Jun. 30, 2018	435,580	$ 591	469,412	27,278	(61,701)
Balance at (in shares) at Jun. 30, 2018		59,080,387
Balance at at Dec. 31, 2018	$ 436,438	$ 591	471,158	56,051	(91,362)
Balance at (in shares) at Dec. 31, 2018	59,134,173	59,134,173
Stock-based compensation plans
Grant of restricted stock	$ 0	$ 2	(2)
Grant of restricted stock (in shares)		143,800
Issuance of common shares, net of withholdings	(1,496)	$ 1	(1,497)
Withholdings of common shares, net of issuances (in shares)		87,166
Forfeited restricted stock	0	$ 0	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification | Accounting Standards Update 2018-07 [Member]	(71,358)			(71,358)
Forfeited restricted stock (in shares)		(1,300)
Amortization of stock awards and restricted stock	3,394		3,394
NET EARNINGS	(3,936)
Total comprehensive income (loss)	3,831			(3,936)	7,767
Balance at at Jun. 30, 2019	$ 370,809	$ 594	473,053	(19,243)	(83,595)
Balance at (in shares) at Jun. 30, 2019	59,363,839	59,363,839
Balance at at Mar. 31, 2019	$ 390,814	$ 594	471,245	7,358	(88,383)
Balance at (in shares) at Mar. 31, 2019		59,351,326
Stock-based compensation plans
Grant of restricted stock	0	$ 0	0
Grant of restricted stock (in shares)		18,600
Issuance of common shares, net of withholdings	(112)	$ 0	(112)
Withholdings of common shares, net of issuances (in shares)		(4,787)
Forfeited restricted stock	0	$ 0	0
Forfeited restricted stock (in shares)		(1,300)
Amortization of stock awards and restricted stock	1,920		1,920
NET EARNINGS	(26,601)
Total comprehensive income (loss)	(21,813)			(26,601)	4,788
Balance at at Jun. 30, 2019	$ 370,809	$ 594	$ 473,053	$ (19,243)	$ (83,595)
Balance at (in shares) at Jun. 30, 2019	59,363,839	59,363,839