Debt and Preferred Equity Investments - Narrative (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2018 USD ($) loan segment	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Preferred equity investment
Allowance for loan and lease losses		$ 5,750,000	$ 0	$ 0	$ 0
Number of investments marketed for sale | loan		2
Unpaid principal balance		$ 159,900,000
Carrying value		$ 2,099,393,000	$ 2,114,041,000
Number of portfolio segments of financial receivables (segment) | segment		1	1
Additional amount of financing receivables included in other assets		$ 88,800,000	$ 65,500,000
Financing receivable, nonaccrual status		$ 28,400,000
Weighted average risk rating		1.2
Junior Mortgage Participation Acquired in September 2014
Preferred equity investment
Payments to acquire loans receivable	$ 0
Carrying value			$ 0
Financing Receivables, Equal to Greater than 90 Days Past Due
Preferred equity investment
Financing receivable, past due		$ 0