Information Concerning Guarantor and Non-Guarantor Subsidiaries (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
Net cash provided by (used in) continuing operating activities	$ 79,099	$ 39,650
Net cash provided by discontinued operating activities	51	(28)
Net cash provided by (used in) operating activities	79,150	39,622
Purchases of property and equipment	(58,788)	(61,413)
Collection of notes receivable	2,870	2,465
Other investing activities	424	2,183
Net cash used in investing activities - continuing operations	(55,494)	(56,765)
Net cash used investing activities - discontinued operations
Net cash used in investing activities	(55,494)	(56,765)
Repayments under credit facility	(45,000)
Proceeds from exercise of stock option and purchase plans	6,833	4,193
Other financing activities, net	(373)	(85)
Net cash used in financing activities - continuing operations	(38,540)	4,108
Net cash provided by financing activities - discontinued operations
Net cash used in financing activities	(38,540)	4,108
Net change in cash and cash equivalents	(14,884)	(13,035)
Cash and cash equivalents - unrestricted, beginning of period	44,388	124,398
Cash and cash equivalents - unrestricted, end of period	29,504	111,363
Issuer [Member]
CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
Net cash provided by (used in) continuing operating activities	32,560	(12,553)
Net cash provided by (used in) operating activities	32,560	(12,553)
Purchases of property and equipment	(6,111)	(2,247)
Other investing activities		4
Net cash used in investing activities - continuing operations	(6,111)	(2,243)
Net cash used investing activities - discontinued operations
Net cash used in investing activities	(6,111)	(2,243)
Repayments under credit facility	(45,000)
Proceeds from exercise of stock option and purchase plans	6,833	4,193
Net cash used in financing activities - continuing operations	(38,167)	4,193
Net cash provided by financing activities - discontinued operations
Net cash used in financing activities	(38,167)	4,193
Net change in cash and cash equivalents	(11,718)	(10,603)
Cash and cash equivalents - unrestricted, beginning of period	37,562	117,913
Cash and cash equivalents - unrestricted, end of period	25,844	107,310
Guarantor [Member]
CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
Net cash provided by (used in) continuing operating activities	46,590	52,137
Net cash provided by discontinued operating activities		38
Net cash provided by (used in) operating activities	46,590	52,175
Purchases of property and equipment	(52,677)	(59,166)
Collection of notes receivable	2,870	2,465
Other investing activities	424	2,179
Net cash used in investing activities - continuing operations	(49,383)	(54,522)
Net cash used investing activities - discontinued operations
Net cash used in investing activities	(49,383)	(54,522)
Other financing activities, net	(373)	(85)
Net cash used in financing activities - continuing operations	(373)	(85)
Net cash provided by financing activities - discontinued operations
Net cash used in financing activities	(373)	(85)
Net change in cash and cash equivalents	(3,166)	(2,432)
Cash and cash equivalents - unrestricted, beginning of period	6,826	6,485
Cash and cash equivalents - unrestricted, end of period	3,660	4,053
Non-Guarantor [Member]
CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
Net cash provided by (used in) continuing operating activities	(51)	66
Net cash provided by discontinued operating activities	51	(66)
Net cash used investing activities - discontinued operations
Net cash provided by financing activities - discontinued operations
Eliminations [Member]
CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS
Net cash provided by (used in) continuing operating activities
Net cash provided by discontinued operating activities
Net cash provided by (used in) operating activities
Purchases of property and equipment
Collection of notes receivable
Other investing activities
Net cash used in investing activities - continuing operations
Net cash used investing activities - discontinued operations
Net cash used in investing activities
Repayments under credit facility
Proceeds from exercise of stock option and purchase plans
Other financing activities, net
Net cash used in financing activities - continuing operations
Net cash provided by financing activities - discontinued operations
Net cash used in financing activities
Net change in cash and cash equivalents
Cash and cash equivalents - unrestricted, beginning of period
Cash and cash equivalents - unrestricted, end of period