Commitments and Contingencies - Additional Information (Details) shares in Thousands, ¥ in Billions		2 Months Ended	12 Months Ended
	Jul. 01, 2018 ft² Floor	Mar. 02, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2019 JPY (¥)	Jun. 24, 2016 USD ($)	Jul. 31, 2015 USD ($) shares
Other Commitments [Line Items]
Rental Expense Relating to Operating Leases			$ 43,893,000	$ 39,485,000	$ 33,405,000
Other Assets			89,480,000	65,073,000
Additional Floors | Floor	7
Additional Floors Commencing on Lease Effective Date | Floor	3
Time to Take Possession of Additional Floors	5 years
Square Feet of Office Space | ft²	350,000
Unfunded Commitments for Capital Contributions			15,244,000
Contractual Obligations Related To Tax Receivable Agreements			103,572,000
Payment To Counterparties To Tax Receivable Agreement Within One Year Or Less			9,161,000
Payment To Counterparties To Tax Receivable Agreement One To Three Years			19,304,000
Payment To Counterparties To Tax Receivable Agreement Three To Five Years			20,002,000
Payment To Counterparties To Tax Receivable Agreement After Five Years			$ 55,105,000
Underwritten Shares (in shares) | shares									294
Aggregate Offering Price									$ 30,800,000
Inter-Bank Balance Interest Rate [Member]
Other Commitments [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.10%
Subsequent Event [Member] | Foreign Exchange Forward [Member]
Other Commitments [Line Items]
Derivative Asset, Notional Amount						$ 35,598,000	¥ 3.8
PNC Bank [Member]
Other Commitments [Line Items]
Maximum Borrowing Capacity								$ 30,000,000
Amount Outstanding During Period		$ 30,000,000
BBVA Bancomer [Member]
Other Commitments [Line Items]
Maximum Borrowing Capacity			$ 10,175,000
Office Equipment [Member]
Other Commitments [Line Items]
Rental Expense Relating to Operating Leases			3,338,000	2,394,000	$ 2,449,000
Letter of Credit [Member]
Other Commitments [Line Items]
Other Assets			$ 5,502,000	$ 5,398,000