Earnings Per Share - Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock options and assumed options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted weighted average common shares outstanding (in shares)	258,917	197,350	522,997
Restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted weighted average common shares outstanding (in shares)	129	0	0
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted weighted average common shares outstanding (in shares)	188,050	25,640	0
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted weighted average common shares outstanding (in shares)	13,281	29,835	96,368