Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under U.S. GAAP Guidance (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Marketable securities	$ 33,283	$ 36,795
Loans held for sale, at fair value	1,086,805	215,290
Debt securities	12,754	0
Total assets	1,174,330	325,011
Liabilities:
Contingent consideration	31,481	45,172
Total Liabilities	49,429	70,833
Rate lock commitments
Assets:
Derivative asset	21,034	32,035
Liabilities:
Derivative liability	2,977	12,124
Nasdaq Forwards
Assets:
Derivative asset	12,822	26,502
Forward sale contracts
Assets:
Derivative asset	7,632	14,389
Liabilities:
Derivative liability	14,971	13,537
Level 1
Assets:
Marketable securities	33,283	36,795
Loans held for sale, at fair value	0	0
Debt securities	0
Total assets	33,283	36,795
Liabilities:
Contingent consideration	0	0
Total Liabilities	0	0
Level 1 | Rate lock commitments
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 1 | Nasdaq Forwards
Assets:
Derivative asset	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	1,086,805	215,290
Debt securities	12,754
Total assets	1,099,559	215,290
Liabilities:
Contingent consideration	0	0
Total Liabilities	0	0
Level 2 | Rate lock commitments
Assets:
Derivative asset	0	0
Liabilities:
Derivative liability	0	0
Level 2 | Nasdaq Forwards
Assets:
Derivative asset	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
Debt securities	0
Total assets	41,488	72,926
Liabilities:
Contingent consideration	31,481	45,172
Total Liabilities	49,429	70,833
Level 3 | Rate lock commitments
Assets:
Derivative asset	21,034	32,035
Liabilities:
Derivative liability	2,977	12,124
Level 3 | Nasdaq Forwards
Assets:
Derivative asset	12,822	26,502
Level 3 | Forward sale contracts
Assets:
Derivative asset	7,632	14,389
Liabilities:
Derivative liability	$ 14,971	$ 13,537