Net Income per Common Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Income per Common Share
Weighted average shares used for the basic net income per share computation	284,928,969	272,588,332	284,469,689	268,024,691
Incremental shares from share-based compensation	126,265	194,133	137,625	228,142
Weighted average shares used for diluted net income per share computation	285,372,256	273,099,487	284,924,336	268,569,855
Unvested Shares
Net Income per Common Share
Unvested shares from share-based compensation that were anti-dilutive	237,861	44,191	164,111	32,016
Convertible Partnership Units
Net Income per Common Share
Weighted average partnership common units convertible to common shares that were dilutive	317,022	317,022	317,022	317,022
Unvested shares from share-based compensation that were anti-dilutive	359,980	88,182	207,948	88,182