Share-Based Compensation - Unvested RSAs Outstanding (Details) - RSAs	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of Shares
Unvested RSAs, Beginning Balance (in shares) | shares	328,347
Granted (in shares) | shares	132,710
Forfeited (in shares) | shares	(4,702)
Vested (in shares) | shares	(89,362)
Unvested RSAs, Ending Balance (in shares) | shares	366,993
Weighted-Average Grant Date Fair Value
Unvested RSAs, Beginning Balance (in dollars per share) | $ / shares	$ 22.87
Granted (in dollars per share) | $ / shares	40.47
Forfeited (in dollars per share) | $ / shares	23.63
Vested (in dollars per share) | $ / shares	20.53
Unvested RSAs, Ending Balance (in dollars per share) | $ / shares	$ 29.79