INVESTMENTS - Equity-method Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Assets:
Cash and cash-equivalents	$ 2,913,015		$ 2,913,015		$ 3,713,045
Investments, at fair value	42,048,647		42,048,647		43,084,842
Other assets	2,193,194		2,193,194		1,994,304
Total assets	47,154,856		47,154,856		48,792,191
Liabilities and Capital:
Debt obligations	8,445,799		8,445,799		7,372,063
Other liabilities	2,361,925		2,361,925		2,028,065
Total liabilities	10,807,724		10,807,724		9,400,128
Total capital	36,347,132		36,347,132		39,392,063
Total liabilities and capital	47,154,856		47,154,856		$ 48,792,191
Statements of Operations:
Revenues / investment income	387,281	$ 607,105	1,464,961	$ 1,632,204
Interest expense	(62,636)	(48,851)	(167,507)	(129,020)
Other expenses	(205,998)	(207,052)	(618,255)	(644,791)
Net realized and unrealized gain on investments	1,066,616	1,771,018	2,933,914	2,609,742
Net income	$ 1,185,263	$ 2,122,220	$ 3,613,113	$ 3,468,135