Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under U.S. GAAP Guidance (Detail) - USD ($)	Dec. 31, 2019	Nov. 30, 2019	Dec. 31, 2018
Assets:
Marketable securities	$ 36,795,000	$ 98,600,000	$ 48,942,000
Derivative contract, Assets	72,926,000		92,528,000
Loans held for sale, at fair value	215,290,000		990,864,000
Total assets	325,011,000		1,132,334,000
Liabilities:
Accounts payable, accrued expenses and other liabilities—contingent consideration	45,172,000		32,551,000
Derivative contract, Liabilities	25,661,000		16,678,000
Total Liabilities	70,833,000		49,229,000
Nasdaq Forwards
Assets:
Derivative contract, Assets	26,502,000		77,619,000
Rate lock commitments
Assets:
Derivative contract, Assets	32,035,000		6,732,000
Liabilities:
Derivative contract, Liabilities	12,124,000		7,470,000
Forward Sale Contracts
Assets:
Derivative contract, Assets	14,389,000		8,177,000
Liabilities:
Derivative contract, Liabilities	13,537,000		9,208,000
Level 1
Assets:
Marketable securities	36,795,000
Loans held for sale, at fair value	0		0
Total assets	36,795,000		48,942,000
Liabilities:
Accounts payable, accrued expenses and other liabilities—contingent consideration	0		0
Total Liabilities	0		0
Level 1 | Nasdaq Forwards
Assets:
Derivative contract, Assets	0		0
Level 1 | Rate lock commitments
Assets:
Derivative contract, Assets	0		0
Liabilities:
Derivative contract, Liabilities	0		0
Level 1 | Forward Sale Contracts
Assets:
Derivative contract, Assets	0		0
Liabilities:
Derivative contract, Liabilities	0		0
Level 2
Assets:
Marketable securities	0		0
Loans held for sale, at fair value	215,290,000		990,864,000
Total assets	215,290,000		990,864,000
Liabilities:
Accounts payable, accrued expenses and other liabilities—contingent consideration	0		0
Total Liabilities	0		0
Level 2 | Nasdaq Forwards
Assets:
Derivative contract, Assets	0		0
Level 2 | Rate lock commitments
Assets:
Derivative contract, Assets	0		0
Liabilities:
Derivative contract, Liabilities	0		0
Level 2 | Forward Sale Contracts
Assets:
Derivative contract, Assets	0		0
Liabilities:
Derivative contract, Liabilities	0		0
Level 3
Assets:
Marketable securities	0		0
Loans held for sale, at fair value	0		0
Total assets	72,926,000		92,528,000
Liabilities:
Accounts payable, accrued expenses and other liabilities—contingent consideration	45,172,000		32,551,000
Total Liabilities	70,833,000		49,229,000
Level 3 | Nasdaq Forwards
Assets:
Derivative contract, Assets	26,502,000		77,619,000
Level 3 | Rate lock commitments
Assets:
Derivative contract, Assets	32,035,000		6,732,000
Liabilities:
Derivative contract, Liabilities	12,124,000		7,470,000
Level 3 | Forward Sale Contracts
Assets:
Derivative contract, Assets	14,389,000		8,177,000
Liabilities:
Derivative contract, Liabilities	$ 13,537,000		$ 9,208,000