Consolidated Statement of Partners' Capital - USD ($) $ in Thousands	Total	Subsidiaries [Member]	Subsidiaries [Member] Limited Partners' Capital - Preferred [Member]	Subsidiaries [Member] Limited Partners' Capital - Common [Member]	Subsidiaries [Member] General Partner's Capital [Member]	Common Stock [Member]	Common Stock [Member] Subsidiaries [Member]	Common Stock [Member] Subsidiaries [Member] Limited Partners' Capital - Common [Member]	PreferredStock/Units [Member]	PreferredStock/Units [Member] Subsidiaries [Member]	PreferredStock/Units [Member] Subsidiaries [Member] Limited Partners' Capital - Preferred [Member]	PreferredStock/Units [Member] Subsidiaries [Member] Limited Partners' Capital - Common [Member]
Balance at Dec. 31, 2013		$ 1,248,055	$ 351,250	$ 887,695	$ 9,110
Balance, units at Dec. 31, 2013				64,542,901	662,373
Net (loss) income	$ 124,611	124,611		$ 123,362	$ 1,249
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustments	$ 0	0
Common unit distributions		(119,697)		(118,723)	(974)
Preferred unit distributions		$ (27,245)		$ (26,972)	(273)
Issuance of OP units to DFT when redeemable partnership units redeemed, units	234,300	234,300		234,300
Redemption of operating partnership units	$ 6,100	$ 6,100		$ 6,100		$ 0
Issuance of OP units for stock awards, units				163,187
Issuance of OP units for stock awards		360		$ 360
Issuance of OP units due to option exercises, units				507,056
Issuance of OP units due to option exercises		5,556		$ 5,556
Retirement and forfeiture of OP units, units				(48,013)
Retirement and forfeiture of OP units		(1,193)		$ (1,193)
Amortization of deferred compensation costs	6,565	6,565		6,565
Adjustments to redeemable partnership units		(131,989)		(130,496)	(1,493)
Balance at Dec. 31, 2014		1,111,123	351,250	$ 752,254	$ 7,619
Balance, units at Dec. 31, 2014				65,399,431	662,373
Net (loss) income	(4,086)	(4,086)		$ (4,045)	$ (41)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustments	$ 0	0
Common unit distributions		(139,963)		(138,817)	(1,146)
Preferred unit distributions		$ (27,245)		$ (26,972)	(273)
Issuance of OP units to DFT when redeemable partnership units redeemed, units	363,674	363,674		363,674
Redemption of operating partnership units	$ 9,544	$ 9,544		$ 9,544		0
Retirement of OP units for common stock repurchase, units				(1,002,610)
Retirement of OP units for common stock repurchases		(31,912)		$ (31,912)
Issuance of OP units for stock awards, units				565,162
Issuance of OP units for stock awards		2,239		$ 2,239
Issuance of OP units due to option exercises, units				362,642
Issuance of OP units due to option exercises		7,930		$ 7,930
Retirement and forfeiture of OP units, units				(245,022)
Retirement and forfeiture of OP units		(7,682)		$ (7,682)
Amortization of deferred compensation costs	7,846	7,846		7,846
Adjustments to redeemable partnership units		24,404		24,542	(138)
Balance at Dec. 31, 2015		952,198	351,250	$ 594,927	$ 6,021
Balance, units at Dec. 31, 2015				65,443,277	662,373
Net (loss) income	181,447	181,447		$ 179,864	$ 1,583
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustments	$ (1,257)	(1,257)		(1,246)	(11)
Stock Issued During Period, Shares, New Issues	7,613,000							7,613,000
Stock Issued During Period, Value, New Issues	$ 275,470					8	$ 275,470	$ 275,470		$ 194,252	$ 201,250	$ 6,998
Common unit distributions		(170,668)		(169,403)	(1,265)
Preferred unit distributions		$ (20,739)		$ (20,558)	(181)
Issuance of OP units to DFT when redeemable partnership units redeemed, units	1,618,048	1,618,048		1,618,048
Redemption of operating partnership units	$ 64,169	$ 64,169		$ 64,169		$ 2
Stock Redeemed or Called During Period, Value	351,250	351,250	351,250						$ 351,250
Issuance of OP units for stock awards, units				227,430
Issuance of OP units for stock awards		810		$ 810
Issuance of OP units due to option exercises, units				478,733
Issuance of OP units due to option exercises		10,592		$ 10,592
Retirement and forfeiture of OP units, units				(128,098)
Retirement and forfeiture of OP units		(2,969)		$ (2,969)
Amortization of deferred compensation costs	$ 6,813	6,813		6,813
Adjustments to redeemable partnership units		(176,081)		(176,579)	498
Balance at Dec. 31, 2016		$ 962,787	$ 201,250	$ 754,892	$ 6,645
Balance, units at Dec. 31, 2016				75,252,390	662,373