Earnings Per Common Share Calculation of Numerator and Denominator in EPS table (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Earnings Per Share Disclosure [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio											2
Numerators:
Consolidated income from continuing operations	$ 39,767	$ 42,106	$ 36,826	$ 31,813	$ 34,262	$ 30,276	$ 30,040	$ 43,890	$ 150,512	$ 138,468	$ 77,247
Amounts allocated to dilutive securities									11,141	10,463	9,706
Preferred Stock distributions									9,226	9,274	9,280
Net Income (Loss) Available to Common Stockholders, Basic									130,145	118,731	106,919
Income from continuing operations available to Common Stockholders – fully diluted									11,141	10,463	9,706
Net Income (Loss) Available to Common Stockholders, Diluted									141,286	129,194	116,625
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									$ 0	$ 0	$ 44,569
Denominator:
Weighted average Common Stockholders outstanding—basic | shares	84,072	84,057	84,031	83,961	83,562	83,531	83,234	83,116	84,031	83,362	83,018
Effect of dilutive securities:
Redemption of Common OP Units for Common Stockholders | shares									7,216	7,411	7,549
Stock options and restricted Stockholders | shares									660	738	629
Weighted average Common Stockholders outstanding—fully diluted | shares	91,875	91,940	91,851	91,777	91,644	91,528	91,420	91,353	91,907	91,511	91,196
Earnings per Common Share – Basic:
Income from continuing operations | $ / shares									$ 1.55	$ 1.42	$ 0.75
Income from discontinued operations | $ / shares									0.00	0.00	0.54
Net income available for Common Stockholders | $ / shares	$ 0.41	$ 0.44	$ 0.38	$ 0.32	$ 0.35	$ 0.31	$ 0.31	$ 0.46	1.55	1.42	1.29
Earnings per Common Share – Fully Diluted:
Income from continuing operations | $ / shares									1.54	1.41	0.75
Income from discontinued operations | $ / shares									0.00	0.00	0.53
Net income available for Common Stockholders | $ / shares	$ 0.41	$ 0.43	$ 0.38	$ 0.32	$ 0.35	$ 0.31	$ 0.30	$ 0.46	$ 1.54	$ 1.41	$ 1.28
Continuing Operations [Member]
Numerators:
Amounts allocated to dilutive securities									$ 11,141	$ 10,463	$ 5,617
Net Income (Loss) Available to Common Stockholders, Basic									130,145	118,731	62,350
Income from continuing operations available to Common Stockholders – fully diluted									11,141	10,463	5,617
Net Income (Loss) Available to Common Stockholders, Diluted									$ 141,286	$ 129,194	$ 67,967