Impairments - Equity Method Investments (Details) $ in Thousands, £ in Millions	3 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 GBP (£)	Sep. 30, 2015 USD ($)
Investment Impairments
Held-to-maturity debt securities, principal balance			$ 68,630	$ 102,958
Four Seasons | Discounted cash flow valuation technique | Level 2
Investment Impairments
Impairments of investments in unconsolidated joint ventures	$ 70,000	$ 42,000
Held-to-maturity debt securities, principal balance					£ 66	$ 100,000