Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended					12 Months Ended
	Dec. 02, 2019 shares	Dec. 31, 2019 USD ($)	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 26, 2018 contract
Accounting Policies [Line Items]
Mortgage servicing rights, serving fee		0.03%					0.03%
Mortgage servicing rights, surveillance fee		0.01%					0.01%
Allowance for doubtful accounts		$ 11,800,000				$ 16,300,000	$ 11,800,000	$ 16,300,000
Goodwill impairment loss							$ 0	$ 0
Payout period for post-termination awards							4 years
Percentage to preferred units		0.6875%	0.6875%	0.6875%	0.6875%	0.6875%	2.75%
Shares settled (in shares) | shares	898,685
Software, including software development costs | Minimum
Accounting Policies [Line Items]
Fixed assets, estimated useful lives							3 years
Software, including software development costs | Maximum
Accounting Policies [Line Items]
Fixed assets, estimated useful lives							5 years
Computer and communications equipment | Minimum
Accounting Policies [Line Items]
Fixed assets, estimated useful lives							3 years
Computer and communications equipment | Maximum
Accounting Policies [Line Items]
Fixed assets, estimated useful lives							5 years
Nasdaq Forwards
Accounting Policies [Line Items]
Number of derivative contracts | contract									4
Warehouse Facilities
Accounting Policies [Line Items]
Debt repayment period							45 days