Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2016

Accounting Policies [Abstract]

Assets Measured at Fair Value on Recurring Basis

Following are the major categories of assets measured at fair value on a recurring basis as of June 30, 2016 and December 31, 2015, using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3) (in thousands):

June 30, 2016	Level 1		Level 2		Level 3		Total
Cash equivalents	$	56,220	$	—	$	—	$	56,220
Commercial paper		—		33,336		—		33,336
Marketable securities - U.S. government		—		6,017		—		6,017
Marketable securities - corporate bonds		—		46,599		—		46,599
	$	56,220	$	85,952	$	—	$	142,172
December 31, 2015	Level 1		Level 2		Level 3		Total
Cash equivalents	$	29,166	$	—	$	—	$	29,166
Commercial paper		—		2,996		—		2,996
Marketable securities - U.S. government		—		11,500		—		11,500
Marketable securities - corporate bonds		—		169,824		—		169,824
	$	29,166	$	184,320	$	—	$	213,486