Equity Investments - Summary of Unaudited Income Statement Information of Equity Method Investee (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended								6 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jul. 09, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statements:
Rental income											$ 570,382	$ 691,699	$ 763,262
Tenant reimbursements and other income											144,509	170,158	189,767
Total revenues		$ 138,934	$ 159,208	$ 203,694	$ 213,055	$ 212,808	$ 216,595	$ 215,194	$ 217,260		714,891	861,857	953,029
Operating expenses											324,948	387,982	410,045
General and administrative											57,457	113,155	80,504
Total expenses											593,568	913,741	849,522
Operating income (loss)											121,323	(51,884)	103,507
Interest expense											(107,316)	(143,230)	(173,011)
Gain (loss) on early extinguishment of debt	$ (60,000)										6,661	4,909	(60,052)
Income (loss) from continuing operations before income taxes and equity in earnings of investees											102,221	(63)	(60,438)
Income tax expense											(2,364)	(3,191)	(2,634)
Equity in earnings of investees											0	24,460	25,754
Net income (loss)											$ 99,857	$ 24,012	$ (156,967)
Weighted average common shares outstanding (in shares)											128,621	125,163	112,378
Net income per common share (in dollars per share)		$ 0.29	$ 0.18	$ 0.04	$ 0.05	$ (1.28)	$ 1.16	$ (0.14)	$ 0.08		$ 0.56	$ (0.19)	$ (1.97)
SIR
Income Statements:
Rental income										$ 98,226			$ 159,011
Tenant reimbursements and other income										16,980			29,312
Total revenues										115,206			188,323
Operating expenses										20,982			36,382
Depreciation and amortization										20,832			31,091
Acquisition related costs										374			2,002
General and administrative										7,731			12,423
Total expenses										49,919			81,898
Operating income (loss)										65,287			106,425
Interest expense										(7,287)			(13,763)
Gain (loss) on early extinguishment of debt										243			0
Income (loss) from continuing operations before income taxes and equity in earnings of investees										58,243			92,662
Income tax expense										(90)			96
Equity in earnings of investees										32			334
Net income (loss)										$ 58,185			$ 93,092
Weighted average common shares outstanding (in shares)										52,394			44,565
Net income per common share (in dollars per share)										$ 1.11			$ 2.09