Income Taxes (Deferred Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred Taxes Assets [Abstract]
Allowance for uncollectible accounts	$ 841	$ 1,315
Accrued assets and other	3,562	1,800
Valuation allowances	(1,491)	(925)
Total current deferred tax assets	2,912	2,190
Share-based compensation	9,138	8,945
Interest on unrecognized tax benefits	456	533
Accrued liabilities and other	2,951	2,242
Operating and capital loss carryforwards	7,624	4,155
Valuation allowances	(6,133)	(4,045)
Total non-current deferred tax assets	14,036	11,830
Total deferred tax assets	16,948	14,020
Deferred Tax Liabilities [Abstract]
Prepaid expenses	783	681
Property and equipment, principally due to differences in depreciation	4,143	2,255
Goodwill, principally due to differences in amortization	124,060	99,664
Total deferred tax liabilities	128,986	102,600
Net deferred tax liabilities	$ 112,038	$ 88,580