Fair Value Measurements (Tables)

3 Months Ended

Mar. 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 March 31, 2014:

	Quoted prices in active markets (level 1)		Significant other observable inputs (level 2)		Significant unobservable inputs (level 3)		March 31, 2014
Assets
U.S. government debt securities (Note 7)	$	—	$	148,951	$	—	$	148,951
Commercial paper (Note 7)		—		1,999		—		1,999
Certificates of deposit (Note 7)		—		2,017		—		2,017
Equity securities (Note 6)		134,474		34,198		—		168,672
	$	134,474	$	187,165	$	—	$	321,639

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