Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended																										9 Months Ended			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2014 Fair Value Level 1	Dec. 31, 2013 Fair Value Level 1	Sep. 30, 2014 Fair Value Level 1 Retail	Dec. 31, 2013 Fair Value Level 1 Retail	Sep. 30, 2014 Fair Value Level 2 Institutional and Other	Dec. 31, 2013 Fair Value Level 2 Institutional and Other	Sep. 30, 2014 Fair Value Level 3 HMS		Sep. 30, 2014 Fair Value U.S. Treasury Notes Level 1	Dec. 31, 2013 Fair Value U.S. Treasury Notes Level 1	Sep. 30, 2014 Book Value	Dec. 31, 2013 Book Value	Sep. 30, 2014 Book Value HMS		Aug. 01, 2014 Book Value HMS		Sep. 30, 2014 Book Value Retail	Dec. 31, 2013 Book Value Retail	Sep. 30, 2014 Book Value Institutional and Other	Dec. 31, 2013 Book Value Institutional and Other	Sep. 30, 2014 Book Value U.S. Treasury Notes	Dec. 31, 2013 Book Value U.S. Treasury Notes	Sep. 30, 2014 HMS		Dec. 31, 2013 HMS	Sep. 30, 2014 Institutional and Other Minimum	Sep. 30, 2014 Institutional and Other Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Cash and cash equivalents	$ 573,067	$ 830,014	$ 711,089	$ 740,481	$ 573,067	$ 830,014									$ 573,067	$ 830,014
Short-term investments	40,014	50,104											40,014	50,104											40,014	50,104
Long-term debt							1,160,925	1,048,010	539,805	512,635											1,178,250	1,178,250	537,568	537,454
Fair value assumption, interest rate																														0.00%	6.85%
Goodwill	783,280	836,843									34,830	[1]					34,830	[1]	118,800	[1]							34,830		118,830
Loss on impairment	$ (84,000)																										$ (84,000)	[1]

[1] Goodwill with a carrying amount of $118.8 million was written down to its implied fair value of $34.8 million, resulting in an impairment charge of $84.0 million, which was recorded in Loss on impairment of assets in the Consolidated Statement of Operations in the third quarter of 2014. See Note 6 — Intangible Assets for additional information.