Short-term Investments (Tables)

12 Months Ended

Dec. 31, 2012

Investments, Debt and Equity Securities [Abstract]

Schedule of Available-for-sale Securities

Short-term investments, with an original maturity of over 90 days, consisted of the following (in thousands):

	As of December 31, 2012
	Amortized Cost		Unrealized Gain in Accumulated OCI		Unrealized Loss in Accumulated OCI		Aggregate Fair Value
U.S. Treasury securities	244,862		128		—		244,990
Total short-term investments	$	244,862	$	128	$	—	$	244,990

	As of December 31, 2011
	Amortized Cost		Unrealized Gain in Accumulated OCI		Unrealized Loss in Accumulated OCI			Aggregate Fair Value
Equity securities	$	7	$	—	$	(6	)	$	1
U.S. Treasury securities	299,939		32		—			299,971
Total short-term investments	$	299,946	$	32	$	(6	)	$	299,972