Fair Value of Financial Assets and Liabilities - Quantitative Information about Level 3 Fair Value Measurements (Detail) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 74,145	$ 72,926
Liabilities	$ 42,863	25,661
Minimum | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0
Maximum | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	1
Weighted Average | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.985
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingency consideration liability	$ 31,575	$ 45,172
Level 3 | Minimum | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.003	0.003
Level 3 | Minimum | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		0.90
Level 3 | Maximum | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.104	0.104
Level 3 | Maximum | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		1
Level 3 | Weighted Average | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.073	0.086
Level 3 | Weighted Average | Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		0.981
Level 3 | Nasdaq Forwards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 18,959	$ 26,502
Level 3 | Nasdaq Forwards | Minimum | Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		0.257
Derivative asset, measurement input	0.379
Level 3 | Nasdaq Forwards | Maximum | Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		0.348
Derivative asset, measurement input	0.422
Level 3 | Nasdaq Forwards | Weighted Average | Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input		0.322
Derivative asset, measurement input	0.419
Level 3 | Forward Sale Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 9,625	$ 14,389
Liabilities	41,730	13,537
Level 3 | Rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	45,561	32,035
Liabilities	$ 1,133	$ 12,124