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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerators:
Consolidated net income	$ 53,380	$ 59,660	$ 49,169	$ 64,177	$ 47,974	$ 54,865	$ 44,463	$ 63,075	$ 226,386	$ 210,377	$ 187,132
Amounts allocated to dilutive securities									13,774	12,788	13,869
Preferred stock distributions									(16)	(7,685)	(9,226)
Net income available to Common Stockholders—Basic									212,596	189,904	164,037
Amounts allocated to dilutive securities									13,774	12,788	13,869
Net income available to Common Stockholders—Fully Diluted									$ 226,370	$ 202,692	$ 177,906
Denominator:
Weighted average Common Shares outstanding – Basic (shares)	89,570	89,200	88,549	88,524	88,115	87,037	86,763	86,048	88,964	86,997	84,778
Effect of dilutive securities:
Exchange of Common OP Units for Common Shares (shares)									5,793	6,033	7,204
Stock options and restricted stock (shares)									298	395	587
Weighted average Common Shares outstanding – Fully Diluted (shares)	95,577	95,263	94,623	94,577	94,295	93,324	93,063	93,011	95,055	93,425	92,569
Earnings per Common Share – Basic:
Earnings per Common Share – Basic (usd per share)	$ 0.56	$ 0.63	$ 0.52	$ 0.68	$ 0.51	$ 0.56	$ 0.46	$ 0.66	$ 2.39	$ 2.18	$ 1.93
Earnings per Common Share – Fully Diluted:
Earnings per Common Share – Fully Diluted (usd per share)	$ 0.56	$ 0.63	$ 0.52	$ 0.68	$ 0.51	$ 0.56	$ 0.45	$ 0.65	$ 2.38	$ 2.17	$ 1.92