Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2014

Fair Value Disclosures [Abstract]

Summary of Placement in the Fair Value Hierarchy of Financial Assets that are Measured at Fair Value on a Recurring Basis

The following table presents the placement in the fair value hierarchy of financial assets that are measured at fair value on a recurring basis, including the items for which the fair value option has been elected, at June 30, 2014:

	Quoted prices in active markets (level 1)		Significant other observable inputs (level 2)		Significant unobservable inputs (level 3)		June 30, 2014
Assets
U.S. government debt securities (Note 7)	$	—	$	173,072	$	—	$	173,072
Certificates of deposit (Note 7)		—		1,519		—		1,519
Equity securities (Note 6)		109,665		25,230		—		134,895
Total	$	109,665	$	199,821	$	—	$	309,486

The following table presents the placement in the fair value hierarchy of financial assets that are measured at fair value on a recurring basis, including the items for which the fair value option has been elected, at December 31, 2013:

	Quoted prices in active markets (level 1)		Significant other observable inputs (level 2)		Significant unobservable inputs (level 3)		December 31, 2013
Assets
U.S. government debt securities (Note 7)	$	—	$	178,299	$	—	$	178,299
Commercial paper (Note 7)		—		7,997		—		7,997
Certificates of deposit (Note 7)		—		2,265		—		2,265
Equity securities (Note 6)		110,297		31,228		—		141,525
Total	$	110,297	$	219,789	$	—	$	330,086