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Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) included in earnings for investments classified as other.

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Fair Value of Financial Instruments - Valuation for Level 3 Liabilities (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2015	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 6,818,901	$ 6,624,896	$ 6,818,901	$ 8,048,053
Total losses (realized/unrealized)
Included in earnings			(82,650)	(57,687)	(133,245)
Purchases/(Sales)			2,784,377	0	(1,009,942)
Paydowns			(137,164)	(136,318)	(85,965)
Balance at the end of period			9,189,459	6,624,896	6,818,901
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities of consolidated VIEs			9,436,421	6,902,536
Consolidated K-Series
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities of consolidated VIEs			2,800,000
PO Security
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sale of investments	$ 44,300
Gain on sale of investments	1,500
Multi-family loans held in securitization trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deconsolidation	1,100,000	$ 0	0		1,075,529
Multi-family collateralized debt obligations, at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deconsolidation	$ 1,000,000		$ 0	$ 0	$ 1,009,942