Cash and Cash Equivalents, Restricted Cash and Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Cash and cash equivalents:
Cash	$ 209,538	$ 86,074
Total Cash and cash equivalents	336,328	186,342	196,848	254,418
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds	88,619	88,769
Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents:
Commercial paper	$ 38,171	$ 11,499