Earnings Per Common Share Calculation of Numerator and Denominator in EPS table (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerators:
Consolidated net income	$ 47,974	$ 54,865	$ 44,463	$ 63,075	$ 42,381	$ 46,757	$ 40,804	$ 57,190	$ 210,377	$ 187,132	$ 150,512
Amounts allocated to dilutive securities									12,788	13,869	11,141
Preferred Stock distributions									(7,685)	(9,226)	(9,226)
Net income available to Common Stockholders – basic									189,904	164,037	130,145
Net income available to Common Stockholders – fully diluted									12,788	13,869	11,141
Net Income (Loss) Available to Common Stockholders, Diluted									$ 202,692	$ 177,906	$ 141,286
Denominator:
Weighted average Common Shares outstanding – basic (shares)	88,115	87,037	86,763	86,048	85,163	85,105	84,516	84,321	86,997	84,778	84,031
Effect of dilutive securities:
Redemption of Common OP Units for Common Stockholders (shares)									6,033	7,204	7,216
Stock options and restricted Stockholders (shares)									395	587	660
Weighted average Common Shares outstanding – fully diluted (shares)	94,295	93,324	93,063	93,011	92,965	92,910	92,264	92,041	93,425	92,569	91,907
Earnings per Common Share – Basic:
Net income available for Common Stockholders (usd per share)	$ 0.51	$ 0.56	$ 0.46	$ 0.66	$ 0.43	$ 0.48	$ 0.42	$ 0.60	$ 2.18	$ 1.93	$ 1.55
Earnings per Common Share – Fully Diluted:
Net income available for Common Stockholders (usd per share)	$ 0.51	$ 0.56	$ 0.45	$ 0.65	$ 0.43	$ 0.48	$ 0.42	$ 0.60	$ 2.17	$ 1.92	$ 1.54