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	3,568		3,568
NET EARNINGS	73,615
Total comprehensive income (loss)	75,686			73,615	2,071
Balance at at Sep. 30, 2018	470,699	$ 591	470,676	60,381	(60,949)
Balance at (in shares) at Sep. 30, 2018		59,080,387
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
Stock-based compensation plans
Amortization of stock awards and restricted stock	1,264		1,264
NET EARNINGS	33,103			33,103
Total comprehensive income (loss)	33,855
Other comprehensive income (loss), net of tax					752
Balance at at Sep. 30, 2018	470,699	$ 591	470,676	60,381	(60,949)
Balance at (in shares) at Sep. 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)		151,300
Issuance of common shares, net of withholdings	(1,521)	$ 1	(1,522)
Withholdings of common shares, net of issuances (in shares)		86,097
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)		(3,000)
Amortization of stock awards and restricted stock	5,281		5,281
NET EARNINGS	101,392
Total comprehensive income (loss)	112,156			101,392	10,764
Balance at at Sep. 30, 2019	$ 480,996	$ 594	474,915	86,085	(80,598)
Balance at (in shares) at Sep. 30, 2019	59,368,570	59,368,570
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
Stock-based compensation plans
Grant of restricted stock	0	$ 0	0
Grant of restricted stock (in shares)		7,500
Issuance of common shares, net of withholdings	(25)	$ 0	(25)
Withholdings of common shares, net of issuances (in shares)		(1,069)
Forfeited restricted stock	0	$ 0	0
Forfeited restricted stock (in shares)		(1,700)
Amortization of stock awards and restricted stock	1,887		1,887
NET EARNINGS	105,328
Total comprehensive income (loss)	108,325			105,328	2,997
Balance at at Sep. 30, 2019	$ 480,996	$ 594	$ 474,915	$ 86,085	$ (80,598)
Balance at (in shares) at Sep. 30, 2019	59,368,570	59,368,570