Equity Investments - Summary of Income Statement Information of Equity Method Investee (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		0 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jul. 09, 2014 SIR	Sep. 30, 2013 SIR	Jul. 09, 2014 SIR	Sep. 30, 2013 SIR
Income Statements:
Rental income	$ 174,216	$ 170,908	$ 518,663	$ 592,221	$ 4,698	$ 41,169	$ 98,226	$ 117,333
Tenant reimbursements and other income	42,379	43,293	130,386	146,780	923	7,415	16,980	21,057
Total revenues	216,595	214,201	649,049	739,001	5,621	48,584	115,206	138,390
Operating expenses	99,392	102,350	293,824	310,585	1,018	9,287	20,982	26,172
Depreciation and amortization					1,043	8,485	20,832	22,445
Acquisition related costs					0	790	374	1,479
General and administrative	47,450	25,742	96,395	63,454	357	3,208	7,731	8,884
Total expenses	204,055	308,374	576,839	681,123	2,418	21,770	49,919	58,980
Operating income (loss)	12,540	(94,173)	72,210	57,878	3,203	26,814	65,287	79,410
Interest expense	(35,245)	(39,236)	(111,079)	(134,452)	(295)	(3,232)	(7,287)	(10,484)
Gain on early extinguishment of debt	6,699	0	6,699	(60,027)	0	0	243	0
Income before income tax expense and equity in earnings of an investee	156,154	(133,182)	157,642	(69,377)	2,908	23,582	58,243	68,926
Income tax expense	(703)	(785)	(2,166)	(2,527)	0	(52)	(90)	(132)
Equity in earnings of investees	1,072	10,492	24,460	14,913	11	64	32	219
Net income (loss)	$ 156,740	$ (216,207)	$ 182,573	$ (151,666)	$ 2,919	$ 23,594	$ 58,185	$ 69,013
Weighted average common shares outstanding (in shares)	128,880	118,328	123,736	110,353	59,889	49,686	52,394	42,790
Net income per common share (in dollars per share)					$ 0.05	$ 0.47	$ 1.11	$ 1.61