Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 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 December 31, 2014:

	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		December 31, 2014
Assets
U.S. government debt securities (Note 7)	$	—	$	115,335	$	—	$	115,335
Certificates of deposit (Note 7)	—		273		—		273
Equity securities (Note 6)	143,927		20,962		—		164,889
	$	143,927	$	136,570	$	—	$	280,497

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
	$	110,297	$	219,789	$	—	$	330,086