Stockholders' Equity and Equity Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2018

Stockholders Equity Note [Abstract]

Summary of Unvested Restricted Common Stock Activity

Stock-Based Awards. A summary of our unvested restricted common stock activity during the quarter and nine months ended September 30, 2018 is as follows (shares in thousands):

	Quarter Ended					Nine Months Ended
	September 30, 2018					September 30, 2018
	Shares			Weighted- Average Grant Date Fair Value		Shares			Weighted- Average Grant Date Fair Value
Unvested awards, beginning		1,189		$	41.67		1,222		$	36.84
Awards granted		38			37.62		527			46.09
Awards forfeited/cancelled		(28	)		39.95		(107	)		40.12
Awards vested		(40	)		37.96		(483	)		34.55
Unvested awards, ending		1,159		$	41.70		1,159		$	41.70