Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under U.S. GAAP Guidance (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Marketable securities	$ 121,759	$ 36,795
Loans held for sale, at fair value	1,537,734	215,290
Total assets	1,733,638	325,011
Liabilities:
Contingent consideration	31,575	45,172
Total Liabilities	74,438	70,833
Nasdaq Forwards
Assets:
Derivative asset	18,959	26,502
Rate lock commitments
Assets:
Derivative asset	45,561	32,035
Liabilities:
Derivative liability	1,133	12,124
Forward sale contracts
Assets:
Derivative asset	9,625	14,389
Liabilities:
Derivative liability	41,730	13,537
Level 1
Assets:
Marketable securities	121,759	36,795
Loans held for sale, at fair value	0	0
Total assets	121,759	36,795
Liabilities:
Contingent consideration	0	0
Total Liabilities	0	0
Level 1 | Nasdaq Forwards
Assets:
Derivative asset	0	0
Level 1 | Rate lock commitments
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 1 | Forward sale contracts
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 2
Assets:
Marketable securities	0	0
Loans held for sale, at fair value	1,537,734	215,290
Total assets	1,537,734	215,290
Liabilities:
Contingent consideration	0	0
Total Liabilities	0	0
Level 2 | Nasdaq Forwards
Assets:
Derivative asset	0	0
Level 2 | Rate lock commitments
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 2 | Forward sale contracts
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 3
Assets:
Marketable securities	0	0
Loans held for sale, at fair value	0	0
Total assets	74,145	72,926
Liabilities:
Contingent consideration	31,575	45,172
Total Liabilities	74,438	70,833
Level 3 | Nasdaq Forwards
Assets:
Derivative asset	18,959	26,502
Level 3 | Rate lock commitments
Assets:
Derivative asset	45,561	32,035
Liabilities:
Derivative liability	1,133	12,124
Level 3 | Forward sale contracts
Assets:
Derivative asset	9,625	14,389
Liabilities:
Derivative liability	$ 41,730	$ 13,537