Guarantor/Non Guarantor Condensed Consolidated Financial Statements (Cash Flows)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	$ (5,817)	$ 5,131	$ 142,719
Cash flows from investing activities:
Purchases of property and equipment	(63,277)	(32,381)	(159,615)
Proceeds from sale of property and equipment	12,569	7,577	57,674
Proceeds from insurance recoveries	3,344	37	285
Net cash provided by (used in) investing activities	(47,364)	(24,767)	(101,656)
Cash flows from financing activities:
Debt repayments	(120,000)	(71,000)	(60,002)
Proceeds from issuance of debt	245,500	22,000	0
Debt issuance costs	(6,332)	(819)	(1,877)
Proceeds from exercise of options	0	183	781
Proceeds from common stock, net of offering costs	0	65,430	0
Purchase of treasury stock	(533)	(124)	(729)
Intercompany contributions / distributions	0	0	0
Net cash provided by (used in) financing activities	118,635	15,670	(61,827)
Net increase (decrease) in cash, cash equivalents and restricted cash	65,454	(3,966)	(20,764)
Beginning cash, cash equivalents, and restricted cash	10,194	14,160	34,924
Ending cash, cash equivalents, and restricted cash	75,648	10,194	14,160
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	0	0	0
Cash flows from investing activities:
Purchases of property and equipment	431	0	269
Proceeds from sale of property and equipment	(431)	0	(269)
Proceeds from insurance recoveries	0	0	0
Net cash provided by (used in) investing activities	0	0	0
Cash flows from financing activities:
Debt repayments	0	0	0
Proceeds from issuance of debt	0	0
Debt issuance costs	0	0	0
Proceeds from exercise of options		0	0
Proceeds from common stock, net of offering costs		0
Purchase of treasury stock	0	0	0
Intercompany contributions / distributions	0	0	0
Net cash provided by (used in) financing activities	0	0	0
Net increase (decrease) in cash, cash equivalents and restricted cash	0	0	0
Beginning cash, cash equivalents, and restricted cash	0	0	0
Ending cash, cash equivalents, and restricted cash	0	0	0
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	25,492	45,035	147,643
Cash flows from investing activities:
Purchases of property and equipment	(56,556)	(31,049)	(157,336)
Proceeds from sale of property and equipment	12,768	7,523	57,444
Proceeds from insurance recoveries	3,344	37	285
Net cash provided by (used in) investing activities	(40,444)	(23,489)	(99,607)
Cash flows from financing activities:
Debt repayments	0	0	(2)
Proceeds from issuance of debt	0	0
Debt issuance costs	0	0	0
Proceeds from exercise of options		0	0
Proceeds from common stock, net of offering costs		0
Purchase of treasury stock	0	0	0
Intercompany contributions / distributions	13,835	(16,698)	(48,130)
Net cash provided by (used in) financing activities	13,835	(16,698)	(48,132)
Net increase (decrease) in cash, cash equivalents and restricted cash	(1,117)	4,848	(96)
Beginning cash, cash equivalents, and restricted cash	(764)	(5,612)	(5,516)
Ending cash, cash equivalents, and restricted cash	(1,881)	(764)	(5,612)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	8,759	(560)	(8,991)
Cash flows from investing activities:
Purchases of property and equipment	(6,407)	(880)	(1,885)
Proceeds from sale of property and equipment	232	54	467
Proceeds from insurance recoveries	0	0	0
Net cash provided by (used in) investing activities	(6,175)	(826)	(1,418)
Cash flows from financing activities:
Debt repayments	0	0	0
Proceeds from issuance of debt	0	0
Debt issuance costs	0	0	0
Proceeds from exercise of options		0	0
Proceeds from common stock, net of offering costs
Purchase of treasury stock	0	0	0
Intercompany contributions / distributions	(381)	(105)	208
Net cash provided by (used in) financing activities	(381)	(105)	208
Net increase (decrease) in cash, cash equivalents and restricted cash	2,203	(1,491)	(10,201)
Beginning cash, cash equivalents, and restricted cash	1,060	2,551	12,752
Ending cash, cash equivalents, and restricted cash	3,263	1,060	2,551
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	(40,068)	(39,344)	4,067
Cash flows from investing activities:
Purchases of property and equipment	(745)	(452)	(663)
Proceeds from sale of property and equipment	0	0	32
Proceeds from insurance recoveries	0	0	0
Net cash provided by (used in) investing activities	(745)	(452)	(631)
Cash flows from financing activities:
Debt repayments	(120,000)	(71,000)	(60,000)
Proceeds from issuance of debt	245,500	22,000
Debt issuance costs	(6,332)	(819)	(1,877)
Proceeds from exercise of options		183	781
Proceeds from common stock, net of offering costs		65,430
Purchase of treasury stock	(533)	(124)	(729)
Intercompany contributions / distributions	(13,454)	16,803	47,922
Net cash provided by (used in) financing activities	105,181	32,473	(13,903)
Net increase (decrease) in cash, cash equivalents and restricted cash	64,368	(7,323)	(10,467)
Beginning cash, cash equivalents, and restricted cash	9,898	17,221	27,688
Ending cash, cash equivalents, and restricted cash	$ 74,266	$ 9,898	$ 17,221