Guarantor/Non Guarantor Condensed Consolidated Financial Statements (Cash Flows (Unaudited)) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities:	$ 121,771	$ 95,487
Cash flows from investing activities:
Purchases of property and equipment	(84,027)	(74,567)
Proceeds from sale of property and equipment	34,538	6,538
Proceeds from insurance recoveries	227	0
Net cash used in investing activities	(49,262)	(68,029)
Cash flows from financing activities:
Debt repayments	(45,002)	(330,013)
Proceeds from issuance of debt	0	320,000
Debt issuance costs	(5)	(6,187)
Tender premium costs	0	(15,381)
Proceeds from exercise of options	753	1,581
Purchase of treasury stock	(711)	(1,132)
Net cash used in financing activities	(44,965)	(31,132)
Net increase (decrease) in cash and cash equivalents	27,544	(3,674)
Beginning cash and cash equivalents	34,924	27,385
Ending cash and cash equivalents	62,468	23,711
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities:	51,325	57,484
Cash flows from investing activities:
Purchases of property and equipment	(82,554)	(63,159)
Proceeds from sale of property and equipment	34,487	6,262
Proceeds from insurance recoveries	227
Net cash used in investing activities	(47,840)	(56,897)
Cash flows from financing activities:
Debt repayments	(2)	(13)
Proceeds from issuance of debt		0
Debt issuance costs	0	0
Tender premium costs		0
Proceeds from exercise of options	0	0
Purchase of treasury stock	0	0
Net cash used in financing activities	(2)	(13)
Net increase (decrease) in cash and cash equivalents	3,483	574
Beginning cash and cash equivalents	(5,516)	(2,059)
Ending cash and cash equivalents	(2,033)	(1,485)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities:	(4,761)	12,748
Cash flows from investing activities:
Purchases of property and equipment	(1,205)	(10,914)
Proceeds from sale of property and equipment	29	276
Proceeds from insurance recoveries	0
Net cash used in investing activities	(1,176)	(10,638)
Cash flows from financing activities:
Debt repayments	0	0
Proceeds from issuance of debt		0
Debt issuance costs	0	0
Tender premium costs		0
Proceeds from exercise of options	0	0
Purchase of treasury stock	0	0
Net cash used in financing activities	0	0
Net increase (decrease) in cash and cash equivalents	(5,937)	2,110
Beginning cash and cash equivalents	12,752	1,076
Ending cash and cash equivalents	6,815	3,186
Eliminations [Member]
Cash flows from financing activities:
Beginning cash and cash equivalents	0
Ending cash and cash equivalents	0
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities:	75,207	25,255
Cash flows from investing activities:
Purchases of property and equipment	(268)	(494)
Proceeds from sale of property and equipment	22	0
Proceeds from insurance recoveries	0
Net cash used in investing activities	(246)	(494)
Cash flows from financing activities:
Debt repayments	(45,000)	(330,000)
Proceeds from issuance of debt		320,000
Debt issuance costs	(5)	(6,187)
Tender premium costs		(15,381)
Proceeds from exercise of options	753	1,581
Purchase of treasury stock	(711)	(1,132)
Net cash used in financing activities	(44,963)	(31,119)
Net increase (decrease) in cash and cash equivalents	29,998	(6,358)
Beginning cash and cash equivalents	27,688	28,368
Ending cash and cash equivalents	$ 57,686	$ 22,010