Schedule IV - Mortgage Loans on Real Estate - Rollforward Reconciliations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Mortgage loans on Real Estate:
Balance at the beginning of the period	$ 2,353,977		$ 2,310,409	$ 1,939,008
Balance at the beginning of the period, provision for loan losses	(4,000)
Origination of mortgage loan receivables	2,873,304		2,098,052	3,557,164
Purchases of mortgage loan receivables	94,079		73,421
Repayment of mortgage loan receivables	(386,852)		(722,360)	(754,760)
Proceeds from sales of mortgage loan receivables	(1,491,092)		(1,440,195)	(2,509,090)
Non-cash disposition of loan via foreclosure				(4,620)
Sale of loans, net	54,046		26,009	71,066
Transfer between held for investment and held for sale	0
Accretion/amortization of discount, premium and other fees	11,180		8,941	12,241
Loan loss provision	0		(300)	(600)
Balance at the end of the period	3,508,642		2,353,977	2,310,409
Balance at the end of the period, provision for loan losses	(4,000)	[1]	(4,000)
Provision for loan losses
Reconciliation of Mortgage loans on Real Estate:
Balance at the beginning of the period, provision for loan losses	(4,000)		(3,700)	(3,100)
Loan loss provision	0		(300)	(600)
Balance at the end of the period, provision for loan losses	(4,000)		(4,000)	(3,700)
Mortgage loan receivables held for sale
Reconciliation of Mortgage loans on Real Estate:
Balance at the beginning of the period	357,882		571,764	417,955
Origination of mortgage loan receivables	1,465,635		1,128,651	2,594,141
Purchases of mortgage loan receivables	0		73,421
Repayment of mortgage loan receivables	(2,569)		(1,768)	(2,308)
Proceeds from sales of mortgage loan receivables	(1,491,092)		(1,440,195)	(2,509,090)
Non-cash disposition of loan via foreclosure				0
Sale of loans, net	54,046		26,009	71,066
Transfer between held for investment and held for sale	(153,722)
Accretion/amortization of discount, premium and other fees	0		0	0
Loan loss provision	0		0	0
Balance at the end of the period	230,180		357,882	571,764
Mortgage loans held by consolidated subsidiaries
Reconciliation of Mortgage loans on Real Estate:
Balance at the beginning of the period	2,000,095		1,742,345	1,524,153
Origination of mortgage loan receivables	1,407,669		969,401	963,023
Purchases of mortgage loan receivables	94,079		0
Repayment of mortgage loan receivables	(384,283)		(720,592)	(752,452)
Proceeds from sales of mortgage loan receivables	0		0	0
Non-cash disposition of loan via foreclosure				(4,620)
Sale of loans, net	0		0	0
Transfer between held for investment and held for sale	153,722
Transfer between held for investment and held for sale	153,722		0	0
Accretion/amortization of discount, premium and other fees	11,180		8,941	12,241
Loan loss provision	0		0	0
Balance at the end of the period	$ 3,282,462		$ 2,000,095	$ 1,742,345

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.