Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended																															3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Money market funds	Dec. 31, 2012 Money market funds	Dec. 31, 2013 Corporate notes, bonds and commercial paper	Dec. 31, 2012 Corporate notes, bonds and commercial paper	Dec. 31, 2013 Total	Dec. 31, 2012 Total	Dec. 31, 2013 Total Money market funds	Dec. 31, 2012 Total Money market funds	Dec. 31, 2013 Total Corporate notes, bonds and commercial paper	Dec. 31, 2012 Total Corporate notes, bonds and commercial paper	Dec. 31, 2013 Level 1	Dec. 31, 2012 Level 1	Dec. 31, 2013 Level 1 Money market funds	Dec. 31, 2012 Level 1 Money market funds	Dec. 31, 2013 Level 1 Corporate notes, bonds and commercial paper	Dec. 31, 2012 Level 1 Corporate notes, bonds and commercial paper	Dec. 31, 2013 Level 2	Dec. 31, 2012 Level 2	Dec. 31, 2013 Level 2 Money market funds	Dec. 31, 2012 Level 2 Money market funds	Dec. 31, 2013 Level 2 Corporate notes, bonds and commercial paper	Dec. 31, 2012 Level 2 Corporate notes, bonds and commercial paper	Dec. 31, 2013 Level 3	Dec. 31, 2012 Level 3	Dec. 31, 2013 Level 3 Money market funds	Dec. 31, 2012 Level 3 Money market funds	Dec. 31, 2013 Level 3 Corporate notes, bonds and commercial paper	Dec. 31, 2012 Level 3 Corporate notes, bonds and commercial paper	Jun. 30, 2013 Nonrecurring basis	Dec. 31, 2013 Nonrecurring basis	Dec. 31, 2012 Nonrecurring basis	Mar. 31, 2013 Nonrecurring basis	Dec. 31, 2013 Nonrecurring basis Level 1	Dec. 31, 2012 Nonrecurring basis Level 1	Dec. 31, 2013 Nonrecurring basis Level 2	Dec. 31, 2012 Nonrecurring basis Level 2	Dec. 31, 2013 Nonrecurring basis Level 3	Dec. 31, 2012 Nonrecurring basis Level 3
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	$ 359,097	$ 183,915		$ 300,605	$ 126,570	$ 58,492	$ 57,345	$ 359,097	$ 183,915	$ 300,605	$ 126,570	$ 58,492	$ 57,345	$ 300,605	$ 126,570	$ 300,605	$ 126,570	$ 0	$ 0	$ 58,492	$ 57,345	$ 0	$ 0	$ 58,492	$ 57,345	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Investment in non-marketable security
Carrying Value																																	600	2,000	2,000
Fair Value																																				0	0	0	0	600	2,000
Impairment of Investment in non-marketable equity security	$ 1,400	$ 0	$ 0																													$ 1,400	$ 1,400	$ 0