Earnings Per Share - Reconciliation of the Average Shares Outstanding Used to Compute Basic and Diluted Earnings per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average shares outstanding - Basic (in shares)	139,998,308	138,972,873	139,853,748	138,866,565
Effect of dilutive securities:
Net effect of dilutive securities (in shares)	1,072,951	1,688,563	1,277,374	1,597,591
Diluted weighted average common shares outstanding (in shares)	141,071,259	140,661,436	141,131,122	140,464,156
Stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	614,882	907,903	670,264	885,705
Unvested restricted stock
Effect of dilutive securities:
Effect of dilutive securities (in shares)	259,300	539,461	410,074	548,887
Unvested performance share units
Effect of dilutive securities:
Effect of dilutive securities (in shares)	198,769	241,199	197,036	162,999