Financial Information for Guarantor Subsidiaries and Non-Guarantor Subsidiaries (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 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	$ 100,403	$ 104,402	$ 118,591	$ 124,281
Accounts receivable, net	177,398	182,467
Inventories	79,825	79,742
Other current assets	41,771	40,502
Property and equipment, net	419,516	426,488
Investment in subsidiaries	0	0
Goodwill	779,567	768,318
Intangible assets	85,351	86,859
Intercompany balances	0	0
Other assets	492,312	473,123
Total assets	2,176,143	2,161,901
Liabilities and stockholders' equity
Current installments of long-term debt	33,819	26,191
Other current liabilities	190,957	210,892
Long-term debt, excluding current installments	1,353,566	1,364,476
Other non-current liabilities	120,217	116,628
Intercompany balances	0	0
Stockholders' equity	477,584	443,714
Total liabilities and stockholders' equity	2,176,143	2,161,901
Parent Company
Assets
Cash and cash equivalents	21,902	24,042
Accounts receivable, net	0	0
Inventories	0	0
Other current assets	8,234	8,699
Property and equipment, net	3,850	3,522
Investment in subsidiaries	542,361	551,256
Goodwill	0	0
Intangible assets	0	0
Intercompany balances	98,616	125,440
Other assets	74,985	17,002
Total assets	749,948	729,961
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	17,098	31,231
Long-term debt, excluding current installments	250,000	250,000
Other non-current liabilities	5,266	5,016
Intercompany balances	0	0
Stockholders' equity	477,584	443,714
Total liabilities and stockholders' equity	749,948	729,961
SGI
Assets
Cash and cash equivalents	298	56
Accounts receivable, net	51,552	53,531
Inventories	23,420	23,714
Other current assets	3,383	3,409
Property and equipment, net	163,167	166,637
Investment in subsidiaries	788,708	721,909
Goodwill	273,656	273,656
Intangible assets	41,527	41,520
Intercompany balances	0	0
Other assets	20,915	82,748
Total assets	1,366,626	1,367,180
Liabilities and stockholders' equity
Current installments of long-term debt	6,280	6,280
Other current liabilities	61,711	56,050
Long-term debt, excluding current installments	1,103,473	1,104,884
Other non-current liabilities	39,112	38,772
Intercompany balances	119,804	71,603
Stockholders' equity	36,246	89,591
Total liabilities and stockholders' equity	1,366,626	1,367,180
Guarantor Subsidiaries
Assets
Cash and cash equivalents	0	0
Accounts receivable, net	37,488	41,238
Inventories	17,503	16,884
Other current assets	6,197	5,117
Property and equipment, net	34,297	36,028
Investment in subsidiaries	0	0
Goodwill	78,618	78,618
Intangible assets	24,730	25,849
Intercompany balances	244,313	231,357
Other assets	14,229	12,265
Total assets	457,375	447,356
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	28,324	30,140
Long-term debt, excluding current installments	0	0
Other non-current liabilities	13,010	13,427
Intercompany balances	0	0
Stockholders' equity	416,041	403,789
Total liabilities and stockholders' equity	457,375	447,356
Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	80,644	81,482
Accounts receivable, net	88,358	87,698
Inventories	38,902	39,144
Other current assets	23,957	23,277
Property and equipment, net	218,202	220,301
Investment in subsidiaries	855,867	909,379
Goodwill	427,293	416,044
Intangible assets	19,094	19,490
Intercompany balances	0	0
Other assets	384,796	367,209
Total assets	2,137,113	2,164,024
Liabilities and stockholders' equity
Current installments of long-term debt	27,539	19,911
Other current liabilities	86,253	94,682
Long-term debt, excluding current installments	93	9,592
Other non-current liabilities	62,829	59,413
Intercompany balances	223,135	285,162
Stockholders' equity	1,737,264	1,695,264
Total liabilities and stockholders' equity	2,137,113	2,164,024
Eliminating Entries
Assets
Cash and cash equivalents	(2,441)	(1,178)
Accounts receivable, net	0	0
Inventories	0	0
Other current assets	0	0
Property and equipment, net	0	0
Investment in subsidiaries	(2,186,936)	(2,182,544)
Goodwill	0	0
Intangible assets	0	0
Intercompany balances	(342,929)	(356,797)
Other assets	(2,613)	(6,101)
Total assets	(2,534,919)	(2,546,620)
Liabilities and stockholders' equity
Current installments of long-term debt	0	0
Other current liabilities	(2,429)	(1,211)
Long-term debt, excluding current installments	0	0
Other non-current liabilities	0	0
Intercompany balances	(342,939)	(356,765)
Stockholders' equity	(2,189,551)	(2,188,644)
Total liabilities and stockholders' equity	$ (2,534,919)	$ (2,546,620)