Equity Investments (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			0 Months Ended	3 Months Ended			3 Months Ended			3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Jul. 02, 2013 SIR	Mar. 31, 2014 SIR	Dec. 31, 2013 SIR	Jul. 02, 2013 SIR Maximum	Mar. 31, 2013 GOV	Mar. 31, 2014 GOV	Dec. 31, 2013 GOV	Mar. 31, 2014 AIC	Mar. 31, 2013 AIC	Dec. 31, 2013 AIC
Equity Investments
Equity method investments, ownership percentage					44.10%	44.20%	50.00%		0.00%	0.00%	12.50%		12.50%
Equity Investments	$ 518,934		$ 517,991		$ 513,099	$ 512,078					$ 5,835		$ 5,913
Equity in Earnings (Loss)	10,934	4,262			11,032			4,111			(98)	151
Equity investments, common shares owned					22,000,000
Equity investments, market value based on quoted market prices					665,940
Equity investments, quoted market price of common share (in dollars per share)					$ 30.27
Market value of common shares exceeding carrying value				17,609
Amortization of the difference between carrying value and share of underlying equity				34 years
Cash distributions					$ 10,120