Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income	$ 217,968	$ 246,440	$ 211,885
Adjustments to reconcile net income to net cash provided by operating activities
Non-cash compensation expense	24,031	21,899	20,717
Amortization of deferred fees on loans	(38,373)	(40,345)	(36,053)
Amortization of deferred financing costs and premiums/discount on debt obligations	21,988	19,339	20,708
Gain on investments at fair value		(13,420)	(21,967)
Income from equity investment in unconsolidated subsidiary		(3,187)	(11,798)
Distributions of income from unconsolidated subsidiary		9,977	5,007
Changes in assets and liabilities, net
Other assets	(4,632)	6,069	(22,385)
Other liabilities	6,479	(10,120)	5,280
Net cash provided by operating activities	227,461	236,652	171,394
Cash flows from investing activities
Origination and fundings of loans receivable	(3,598,166)	(3,151,882)	(7,204,487)
Principal collections and sales proceeds from loans receivable and other assets	2,780,431	3,514,429	2,347,966
Origination and exit fees received on loans receivable	55,441	44,697	33,501
Receipts under derivative financial instruments	6,453	41,573
Payments under derivative financial instruments	(20,870)	(14,730)
Return of collateral deposited under derivative agreements	16,120
Collateral deposited under derivative agreements	(20,161)
Net cash (used in) provided by investing activities	(780,752)	434,087	(4,823,020)
Cash flows from financing activities
Borrowings under secured debt agreements	4,306,301	3,185,933	6,885,393
Repayments under secured debt agreements	(4,778,194)	(3,534,803)	(3,030,091)
Proceeds from issuance of collateralized loan obligations	817,500
Proceeds from sale of loan participations	80,706	54,441	256,000
Repayment of loan participations	(381,310)	(136,000)	(238,164)
Payment of deferred financing costs	(27,465)	(15,350)	(21,230)
Receipts under derivative financial instruments			17,076
Contributions from non-controlling interests	12,165
Distributions to non-controlling interests	(6,162)	(21,070)	(37,428)
Net proceeds from issuance of convertible notes	394,632
Net proceeds from issuance of class A common stock	391,558	27	1,029,540
Dividends paid on class A common stock	(234,989)	(232,775)	(166,978)
Net cash provided by (used in) financing activities	574,742	(699,597)	4,694,118
Net increase (decrease) in cash, cash equivalents, and restricted cash	21,451	(28,858)	42,492
Cash, cash equivalents, and restricted cash at beginning of year	75,567	106,006	63,401
Effects of currency translation on cash, cash equivalents, and restricted cash	5,500	(1,581)	113
Cash, cash equivalents, and restricted cash at end of year	102,518	75,567	106,006
Supplemental disclosure of cash flows information
Payments of interest	(206,966)	(164,905)	(127,429)
Payments of income taxes	(296)	(286)	(125)
Supplemental disclosure of non-cash investing and financing activities
Dividends declared, not paid	(66,888)	(58,615)	(58,095)
Loan principal payments held by servicer, net	15,763	$ 670	$ 118,074
Consolidation of loans receivable of a VIE	500,000
Consolidation of securitized debt obligations of a VIE	$ (474,620)