Condensed Consolidated Statements of Changes in Unitholders' Capital (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2018
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	$ 2,484,788	$ 2,057,076	$ 2,487,717	$ 2,020,617
Cumulative-effect adjustment from adoption of accounting guidance					$ 48,709
Issuance of units	0	173,669	0	393,419
Repurchase and cancellation of units	(27)	(380)	(9,952)	(230,358)
Purchase of non-controlling interests in subsidiary		(2,916)		(2,916)
Deferred tax effect resulting from the purchase of OCGH units				(6,051)
Equity reallocation between controlling and non-controlling interests	0	0	0	0
Capital increase related to equity-based compensation	20,793	14,747	34,005	28,444
Distributions declared	(180,840)	(164,010)	(310,962)	(312,409)
Net income	99,288	72,101	219,486	198,949
Foreign currency translation adjustment, net of tax	(339)	129	3,369	(90)
Unitholders' capital, end of period	2,423,663	2,150,416	2,423,663	2,150,416
Paid-in Capital
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	897,782	866,576	893,043	788,413
Issuance of units	0	0	0	219,750
Repurchase and cancellation of units	(27)	(83)	(7,437)	(227,507)
Purchase of non-controlling interests in subsidiary		(1,320)		(1,320)
Deferred tax effect resulting from the purchase of OCGH units				(6,051)
Equity reallocation between controlling and non-controlling interests	30,440	(75)	36,565	73,755
Capital increase related to equity-based compensation	9,685	6,678	15,709	12,634
Unitholders' capital, end of period	937,880	871,776	937,880	871,776
Retained Earnings
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	94,199	99,789	100,683	80,128
Cumulative-effect adjustment from adoption of accounting guidance					20,355
Distributions declared	(76,587)	(68,331)	(130,325)	(121,757)
Net income	42,444	31,121	89,698	83,853
Unitholders' capital, end of period	60,056	62,579	60,056	62,579
Accumulated Other Comprehensive Income (Loss)
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	2,764	357	1,053	443
Foreign currency translation adjustment, net of tax	(360)	63	1,351	(23)
Unitholders' capital, end of period	2,404	420	2,404	420
Non-controlling Interests in Consolidated Subsidiaries
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	1,089,459	1,079,586	1,092,354	1,121,237
Cumulative-effect adjustment from adoption of accounting guidance					$ 28,354
Repurchase and cancellation of units	0	(297)	(2,515)	(2,851)
Purchase of non-controlling interests in subsidiary		(1,596)		(1,596)
Equity reallocation between controlling and non-controlling interests	(30,440)	75	(36,565)	(73,755)
Capital increase related to equity-based compensation	11,108	8,069	18,296	15,810
Distributions declared	(97,424)	(92,646)	(166,979)	(167,819)
Net income	50,015	41,996	116,130	115,940
Foreign currency translation adjustment, net of tax	21	66	2,018	(67)
Unitholders' capital, end of period	$ 1,022,739	1,035,253	$ 1,022,739	1,035,253
Non-controlling Interests in Consolidated Funds
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period		10,768		30,396
Distributions declared		(3,033)		(22,833)
Net income		(1,016)		(844)
Unitholders' capital, end of period		$ 6,719		$ 6,719
Class A Units | Common Units
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period (in shares)	72,928,000	71,172,000	71,662,000	65,310,000
Issuance of units (in shares)	2,729,000	7,000	4,184,000	6,150,000
Cancellation of units associated with forfeitures (in shares)	(7,000)	(4,000)	(27,000)	(85,000)
Repurchase and cancellation of units (in shares)	(1,000)	0	(170,000)	(200,000)
Unitholders' capital, end of period (in shares)	75,649,000	71,175,000	75,649,000	71,175,000
Class B Units | Common Units
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period (in shares)	86,419,000	86,007,000	85,472,000	90,976,000
Issuance of units (in shares)	418,000	0	1,438,000	114,000
Cancellation of units associated with forfeitures (in shares)	(119,000)	0	119,000
Cancellation of units (in shares)	(2,717,000)		(2,717,000)
Repurchase and cancellation of units (in shares)	0	0	(73,000)	(5,083,000)
Unitholders' capital, end of period (in shares)	84,001,000	86,007,000	84,001,000	86,007,000
Series A Preferred Units | Preferred Stock
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	$ 173,669	$ 0	$ 173,669	$ 0
Issuance of units (in shares)				173,669,000
Issuance of units		173,669
Distributions declared	(2,981)		(5,962)
Net income	2,981		5,962
Unitholders' capital, end of period	173,669	173,669	173,669	$ 173,669
Series B Preferred Units | Preferred Stock
Increase (decrease) in Stockholders' Equity:
Unitholders' capital, beginning of period	226,915	0	226,915	0
Distributions declared	(3,848)		(7,696)
Net income	3,848		7,696
Unitholders' capital, end of period	$ 226,915	$ 0	$ 226,915	$ 0