Financial Information for Guarantor Subsidiaries and Non-Guarantor Subsidiaries (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Financial Information for Guarantor Subsidiaries and Non-Guarantor Subsidiaries [Abstract]
Parent company's percentage ownership of guarantors (as a percent)	100.00%
Assets
Cash and cash equivalents	$ 112,431	$ 104,402	$ 127,256	$ 124,281
Accounts receivable, net	166,882	182,467
Inventories	83,584	79,742
Other current assets	42,964	40,502
Property and equipment, net	402,536	426,488
Investment in subsidiaries	0	0
Goodwill	777,738	768,782
Intangible assets	87,025	86,859
Intercompany balances	0	0
Other assets	450,190	473,123
Total assets	2,123,350	2,162,365
Liabilities and stockholders' equity
Current installments of long-term debt	14,783	26,191
Other current liabilities	192,576	211,356
Long-term debt, excluding current installments	1,354,920	1,364,476
Other non-current liabilities	120,018	116,628
Intercompany balances	0	0
Stockholders’ equity	441,053	443,714
Total liabilities and stockholders’ equity	2,123,350	2,162,365
Parent Company
Assets
Cash and cash equivalents	35,800	24,042
Accounts receivable, net	0	0
Inventories	0	0
Other current assets	6,655	8,699
Property and equipment, net	4,238	3,522
Investment in subsidiaries	522,824	551,256
Goodwill	0	0
Intangible assets	0	0
Intercompany balances	75,950	125,440
Other assets	74,665	17,002
Total assets	720,132	729,961
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	24,101	31,231
Long-term debt, excluding current installments	250,000	250,000
Other non-current liabilities	4,978	5,016
Intercompany balances	0	0
Stockholders’ equity	441,053	443,714
Total liabilities and stockholders’ equity	720,132	729,961
SGI
Assets
Cash and cash equivalents	1,092	56
Accounts receivable, net	48,193	53,531
Inventories	25,681	23,714
Other current assets	4,104	3,409
Property and equipment, net	163,026	166,637
Investment in subsidiaries	768,570	721,909
Goodwill	273,656	273,656
Intangible assets	41,296	41,520
Intercompany balances	0	0
Other assets	19,872	82,748
Total assets	1,345,490	1,367,180
Liabilities and stockholders' equity
Current installments of long-term debt	6,280	6,280
Other current liabilities	50,604	56,050
Long-term debt, excluding current installments	1,102,059	1,104,884
Other non-current liabilities	38,856	38,772
Intercompany balances	112,671	71,603
Stockholders’ equity	35,020	89,591
Total liabilities and stockholders’ equity	1,345,490	1,367,180
Guarantor Subsidiaries
Assets
Cash and cash equivalents	0	0
Accounts receivable, net	34,100	41,238
Inventories	16,024	16,884
Other current assets	4,666	5,117
Property and equipment, net	31,285	36,028
Investment in subsidiaries	0	0
Goodwill	78,618	78,618
Intangible assets	22,745	25,849
Intercompany balances	263,852	231,357
Other assets	14,590	12,265
Total assets	465,880	447,356
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	28,292	30,140
Long-term debt, excluding current installments	0	0
Other non-current liabilities	11,941	13,427
Intercompany balances	0	0
Stockholders’ equity	425,647	403,789
Total liabilities and stockholders’ equity	465,880	447,356
Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	77,547	81,482
Accounts receivable, net	84,589	87,698
Inventories	41,879	39,144
Other current assets	27,539	23,277
Property and equipment, net	203,987	220,301
Investment in subsidiaries	842,791	909,379
Goodwill	425,464	416,508
Intangible assets	22,984	19,490
Intercompany balances	0	0
Other assets	343,677	367,209
Total assets	2,070,457	2,164,488
Liabilities and stockholders' equity
Current installments of long-term debt	8,503	19,911
Other current liabilities	91,580	95,146
Long-term debt, excluding current installments	2,861	9,592
Other non-current liabilities	64,243	59,413
Intercompany balances	227,148	285,162
Stockholders’ equity	1,676,122	1,695,264
Total liabilities and stockholders’ equity	2,070,457	2,164,488
Eliminating Entries
Assets
Cash and cash equivalents	(2,008)	(1,178)
Accounts receivable, net	0	0
Inventories	0	0
Other current assets	0	0
Property and equipment, net	0	0
Investment in subsidiaries	(2,134,185)	(2,182,544)
Goodwill	0	0
Intangible assets	0	0
Intercompany balances	(339,802)	(356,797)
Other assets	(2,614)	(6,101)
Total assets	(2,478,609)	(2,546,620)
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	(2,001)	(1,211)
Long-term debt, excluding current installments	0	0
Other non-current liabilities	0	0
Intercompany balances	(339,819)	(356,765)
Stockholders’ equity	(2,136,789)	(2,188,644)
Total liabilities and stockholders’ equity	$ (2,478,609)	$ (2,546,620)