Equity Investments (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statements:
Rental income									$ 707,380	$ 709,390	$ 601,632
Tenant reimbursements and other income									178,156	172,515	139,712
Total revenues	198,419	198,283	246,181	242,653	231,957	222,632	217,346	209,970	885,536	881,905	741,344
Operating expenses									370,869	356,604	297,408
General and administrative									77,209	46,057	38,221
Total expenses									667,250	618,068	520,058
Operating income									218,286	263,837	221,286
Interest and other income									1,229	1,404	1,662
Interest expense									(173,011)	(201,840)	(191,876)
Income from continuing operations before income tax expense and equity in earnings of investees									52,745	70,360	42,214
Income tax benefit (expense)									(2,634)	(3,207)	(1,347)
Equity in earnings of investees									25,754	11,420	11,377
Income from continuing operations									75,865	78,573	52,244
Net (loss) income									(156,967)	(79,845)	109,984
SIR
Income Statements:
Rental income									159,011	105,559	91,775
Tenant reimbursements and other income									29,312	17,231	16,847
Total revenues									188,323	122,790	108,622
Operating expenses									36,382	23,796	22,946
Depreciation and amortization									31,091	14,860	11,205
Acquisition related costs									2,002	2,470
General and administrative									12,423	8,203	5,528
Total expenses									81,898	49,329	39,679
Operating income									106,425	73,461	68,943
Interest expense									(13,763)	(7,565)
Income from continuing operations before income tax expense and equity in earnings of investees									92,662	65,896	68,943
Income tax benefit (expense)									96	(290)
Equity in earnings of investees									334	269
Net (loss) income									93,092	65,875	68,943
Weighted average common shares outstanding									44,565	27,122
Per common share:
Net income per common share (in dollars per share)									$ 2.09	$ 2.43
Equity method investments, ownership percentage	44.20%								44.20%
GOV
Income Statements:
Total revenues										203,700	168,074
Operating expenses										75,326	62,117
Depreciation and amortization										49,070	37,776
Acquisition related costs										1,614	3,504
General and administrative										11,924	10,469
Total expenses										137,934	113,866
Operating income										65,766	54,208
Interest and other income										29	104
Interest expense										(16,892)	(12,057)
Income from continuing operations before income tax expense and equity in earnings of investees										48,903	42,255
Income tax benefit (expense)										(159)	(203)
Equity in earnings of investees										316	139
Income from continuing operations										49,060	42,191
Income from discontinued operations										900	3,806
Net (loss) income										49,960	45,997
Weighted average common shares outstanding										48,617	43,368
Per common share:
Income from continuing operations (in dollars per share)										$ 1.01	$ 0.97
Income from discontinued operations (in dollars per share)										$ 0.02	$ 0.09
Net income per common share (in dollars per share)										$ 1.03	$ 1.06
AIC
Per common share:
Amount invested in equity investee	5,209								5,209
Combined carrying value of equity method investments	$ 5,913								$ 5,913
Number of other companies which are shareholders of related party	4								4
Equity method investments, ownership percentage	12.50%								12.50%