Cash and Cash Equivalents, Restricted Cash and Marketable Securities (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fixed-income debt securities:
Mature within one year - Amortized Cost		$ 3,004
Mature within one year - Unrealized Gain (Loss)		0
Mature within one year - Estimated Fair Value		3,004
Mature after one year and within three years - Amortized Cost	114,300	54,044
Mature after one year and within three years - Unrealized Gain (Loss)	83	(16)
Mature after one year and within three years - Estimated Fair Value	114,383	54,028
Commercial paper:
Mature within one year - Amortized Cost	49,776	19,615
Mature within one year - Unrealized Gain (Loss)	0	0
Mature within one year - Estimated Fair Value	49,776	19,615
Total - Amortized Cost	164,076	76,663
Total - Unrealized Gain (Loss)	83	(16)
Total - Estimated Fair Value	$ 164,159	$ 76,647