Equity Investments (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended			0 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Jul. 02, 2013 SIR	Sep. 30, 2013 SIR	Sep. 30, 2013 SIR	Mar. 15, 2013 GOV	Sep. 30, 2012 GOV	Sep. 30, 2013 GOV	Sep. 30, 2012 GOV	Dec. 31, 2012 GOV	Sep. 30, 2013 AIC	Sep. 30, 2012 AIC	Sep. 30, 2013 AIC	Sep. 30, 2012 AIC	Dec. 31, 2012 AIC
Equity Investments
Equity method investments, ownership percentage							44.20%	44.20%					18.20%	12.50%		12.50%		25.00%
Equity investments	$ 517,254		$ 517,254		$ 184,711		$ 511,473	$ 511,473					$ 173,452	$ 5,781		$ 5,781		$ 11,259
Equity in Earnings	10,492	2,868	14,913	8,655			10,428	10,428		2,638	4,111	8,231		64	230	374	424
Equity investments, common shares owned							22,000,000	22,000,000	9,950,000
Equity investments, market value based on quoted market prices							567,600	567,600
Equity investments, quoted market price of common share (in dollars per share)							$ 25.80	$ 25.80
Gross proceeds received on issuance or sale of common shares									250,740
Net proceeds received on issuance or sale of common shares									239,576
Common stock price per share (in dollars per share)						$ 28.25			$ 25.20
Ownership percentage after offering						44.20%
Market value of common shares exceeding carrying value						17,590
Amortization of the difference between carrying value and share of underlying equity						27 years
Gain on sale of equity investment			66,293						66,293
Cash distributions						$ 9,680					$ 4,279	$ 12,537
Issuance of shares, net						10,500,000