Property and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and Equipment
Property and equipment at cost	$ 1,695,888,000	$ 1,576,923,000
Less: Accumulated depreciation and amortization	(804,569,000)	(727,372,000)
Property and equipment, net	891,319,000	849,551,000	843,983,000
Depreciation and amortization expense	115,600,000	103,400,000	101,800,000
Land
Property and Equipment
Property and equipment at cost	60,544,000	53,492,000
Buildings and improvements
Property and Equipment
Property and equipment at cost	633,248,000	606,130,000
Equipment
Property and Equipment
Property and equipment at cost	343,832,000	325,569,000
Long-lived assets held for sale		27,000,000
Computer hardware and software
Property and Equipment
Property and equipment at cost	460,931,000	360,389,000
Furniture, fixtures & leasehold improvements
Property and Equipment
Property and equipment at cost	110,106,000	102,768,000
Construction-in-progress
Property and Equipment
Property and equipment at cost	$ 87,227,000	$ 128,575,000