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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerators:
Consolidated net income	$ 42,381	$ 46,757	$ 40,804	$ 57,190	$ 39,767	$ 42,106	$ 36,826	$ 31,813	$ 187,132	$ 150,512	$ 138,468
Amounts allocated to dilutive securities									13,869	11,141	10,463
Preferred Stock distributions									9,226	9,226	9,274
Net income available to Common Stockholders – basic									164,037	130,145	118,731
Net income available to Common Stockholders – fully diluted									13,869	11,141	10,463
Net Income (Loss) Available to Common Stockholders, Diluted									$ 177,906	$ 141,286	$ 129,194
Denominator:
Weighted average Common Shares outstanding – basic (shares)	85,163	85,015	84,516	84,321	84,072	84,057	84,031	83,961	84,778	84,031	83,362
Effect of dilutive securities:
Redemption of Common OP Units for Common Stockholders (shares)									7,204	7,216	7,411
Stock options and restricted Stockholders (shares)									587	660	738
Weighted average Common Shares outstanding – fully diluted (shares)	92,965	92,910	92,264	92,041	91,875	91,940	91,851	91,777	92,569	91,907	91,511
Earnings per Common Share – Basic:
Net income available for Common Stockholders (usd per share)	$ 0.43	$ 0.48	$ 0.42	$ 0.60	$ 0.41	$ 0.44	$ 0.38	$ 0.32	$ 1.93	$ 1.55	$ 1.42
Earnings per Common Share – Fully Diluted:
Net income available for Common Stockholders (usd per share)	$ 0.43	$ 0.48	$ 0.42	$ 0.60	$ 0.41	$ 0.43	$ 0.38	$ 0.32	$ 1.92	$ 1.54	$ 1.41