Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2016

Fair Value Disclosures [Abstract]

Fair Value Measurements of Cash Equivalents and Available-For-Sale Investment Securities

The fair value measurements of the Company’s cash equivalents and available-for-sale investment securities are identified in the following tables (in thousands):

			Fair Value Measurements at Reporting Date Using
	March 31, 2016		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	77,003	$	77,003	$	—	$	—
U.S. Treasury notes		21,738		21,738		—		—
Government sponsored enterprise securities		119,510		—		119,510		—
Corporate debt securities		47,334		—		47,334		—
Commercial paper		186,535		—		186,535		—
	$	452,120	$	98,741	$	353,379	$	—

			Fair Value Measurements at Reporting Date Using
	December 31, 2015		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Money market fund	$	46,437	$	46,437	$	—	$	—
U.S. Treasury notes		8,999		8,999		—		—
Government sponsored enterprise securities		157,623		—		157,623		—
	$	213,059	$	55,436	$	157,623	$	—