Fair Value Measurement - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Total	$ 89,336	[1]	$ 206,542	[1]
Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Total	0		0
Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Total	0		0
Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Total	89,336		206,542
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	89,336		201,542
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	0		0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	0		0
Money Market Funds [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds	89,336		201,542
Commercial paper [Member] | Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds			5,000
Commercial paper [Member] | Fair Value, Inputs, Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds			0
Commercial paper [Member] | Fair Value, Inputs, Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds			0
Commercial paper [Member] | Estimate of Fair Value Measurement [Member]
Assets, Fair Value Disclosure [Abstract]
Money market funds			$ 5,000

[1] The fair values of the senior notes payable and Credit Agreement (as defined under “Credit Agreement” in Note 12) loan are based on borrowing rates available to us for long-term loans with similar terms, average maturities, and credit risk.