Guarantor/Non-Guarantor Condensed Consolidated Financial Statements (Cash Flows (Unaudited)) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Parent [Member]	Jun. 30, 2013 Parent [Member]	Jun. 30, 2014 Guarantor Subsidiaries [Member]	Jun. 30, 2013 Guarantor Subsidiaries [Member]	Jun. 30, 2014 Non-Guarantor Subsidiaries [Member]	Jun. 30, 2013 Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:	$ 95,487	$ 70,677	$ 25,255	$ (34,534)	$ 57,484	$ 102,709	$ 12,748	$ 2,502
Cash flows from investing activities:
Purchases of property and equipment	(74,567)	(112,179)	(494)	(1,602)	(63,159)	(103,574)	(10,914)	(7,003)
Proceeds from sale of property and equipment	6,538	6,059	0	0	6,262	5,357	276	702
Net cash used in investing activities	(68,029)	(106,120)	(494)	(1,602)	(56,897)	(98,217)	(10,638)	(6,301)
Cash flows from financing activities:
Debt repayments	(330,013)	(10,862)	(330,000)	(10,000)	(13)	(862)	0	0
Proceeds from issuance of debt	320,000	40,000	320,000	40,000	0	0	0	0
Debt issuance costs	(6,187)	(13)	(6,187)	(13)	0	0	0	0
Tender premium costs	(15,381)	0	(15,381)		0		0
Proceeds from exercise of options	1,581	789	1,581	789	0	0	0	0
Purchase of treasury stock	(1,132)	(628)	(1,132)	(628)	0	0	0	0
Net cash provided by (used in) financing activities	(31,132)	29,286	(31,119)	30,148	(13)	(862)	0	0
Net increase (decrease) in cash and cash equivalents	(3,674)	(6,157)	(6,358)	(5,988)	574	3,630	2,110	(3,799)
Beginning cash and cash equivalents	27,385	23,733	28,368	18,479	(2,059)	(5,401)	1,076	10,655
Ending cash and cash equivalents	$ 23,711	$ 17,576	$ 22,010	$ 12,491	$ (1,485)	$ (1,771)	$ 3,186	$ 6,856