Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Discounted Cash Flow Valuation Technique [Member] Maximum [Member]	Dec. 31, 2013 Discounted Cash Flow Valuation Technique [Member] Maximum [Member]	Sep. 30, 2014 Discounted Cash Flow Valuation Technique [Member] Minimum [Member]	Dec. 31, 2013 Discounted Cash Flow Valuation Technique [Member] Minimum [Member]	Sep. 30, 2014 Convertible Notes Due 2016 [Member]	Oct. 31, 2011 Convertible Notes Due 2016 [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value Measurement [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value Measurement [Member]
Assets
Money market funds									$ 369,042	$ 145,194					$ 369,042	$ 145,194
Federally-sponsored and corporate debt securities	476,667	857,711									476,667	857,711			476,667	857,711
Total assets									369,042	145,194	476,667	857,711			845,709	1,002,905
Liabilities
Convertible notes due 2016									686,840	593,750					686,840	593,750
Contingent consideration													4,736	6,616	4,736	6,616
Total liabilities									$ 686,840	$ 593,750			$ 4,736	$ 6,616	$ 691,576	$ 600,366
Convertible Senior Notes, stated percentage							1.00%	1.00%
Cost of debt and weighted average cost of capital (as a percent)			16.50%	16.50%	8.70%	8.70%