Stock-Based Compensation - Restricted Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted average grant date fair value
Total stock-based compensation expense (in dollars)	$ 7,137	$ 6,852
Restricted stock
Number of shares
Outstanding at beginning of period (in shares)	1,213,581
Granted (in shares)	388,108
Vested (in shares)	(253,683)
Forfeited (in shares)	(33,371)
Outstanding at end of period (in shares)	1,314,635
Weighted average grant date fair value
Outstanding at beginning of period (in dollars per share)	$ 37.69
Granted (in dollars per share)	67.91
Vested (in dollars per share)	45.23
Forfeited (in dollars per share)	54.96
Outstanding at end of period (in dollars per share	$ 44.72
Total stock-based compensation expense (in dollars)	$ 4,139	$ 2,725
Unrecognized compensation expense (in dollars)	$ 50,368
Weighted average period expected to be recognized	3 years 1 month 24 days