Fair Value Measurements - Narrative (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Fair Value, Transfers Between Level 1 and Level 2 [Abstract]
Assets, level 1 to level 2 transfers, amount	$ 287,400,000	$ 0	$ 287,400,000	$ 0
Assets, level 2 to level 1 transfers, amount	0	0	0	0
Liabilities, level 1 to level 2 transfers, amount	0	0	0	0
Liabilities, level 2 to level 1 transfers, amount	0	0	0	0
Cost Method Investments	36,500,000		36,500,000		32,000,000
Fair value cost method investment subsequent to impairment	2,100,000		2,500,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0	0	0	0
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Transfers Between Level 1 and Level 2 [Abstract]
Cost Method Measured at Fair Value	4,300,000		4,700,000
Liabilities, Fair Value Disclosure	0		0		0
Assets, Fair Value Disclosure	$ 0		$ 0		$ 0