Fair Value of Financial Assets and Liabilities - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Assets, Unobservable Input Reconciliation:
Opening Balance	$ 72,926	$ 92,528
Total realized and unrealized gains (losses) included in Net income	14,986	(4,693)
Issuances	0	0
Settlements	(46,424)	(14,909)
Closing Balance	41,488	72,926
Unrealized gains (losses) outstanding, at end of period	41,488	72,926
Liabilities, Unobservable Input Reconciliation:
Opening Balance	70,833	49,229
Total realized and unrealized gains (losses) included in Net income	6,885	27,948
Issuances	2,221	14,957
Settlements	(30,510)	(21,301)
Closing Balance	49,429	70,833
Unrealized (gains) losses outstanding, at end of period	17,540	27,948
Rate lock commitments
Assets, Unobservable Input Reconciliation:
Opening Balance	32,035	6,732
Total realized and unrealized gains (losses) included in Net income	21,034	32,035
Issuances	0	0
Settlements	(32,035)	(6,732)
Closing Balance	21,034	32,035
Unrealized gains (losses) outstanding, at end of period	21,034	32,035
Liabilities, Unobservable Input Reconciliation:
Opening Balance	12,124	7,470
Total realized and unrealized gains (losses) included in Net income	2,977	12,124
Issuances		0
Settlements	(12,124)	(7,470)
Closing Balance	2,977	12,124
Unrealized (gains) losses outstanding, at end of period	2,977	12,124
Contingent consideration
Liabilities, Unobservable Input Reconciliation:
Opening Balance	45,172	32,551
Total realized and unrealized gains (losses) included in Net income	(11,063)	2,287
Issuances	2,221	14,957
Settlements	(4,849)	(4,623)
Closing Balance	31,481	45,172
Unrealized (gains) losses outstanding, at end of period	(408)	2,287
Forward sale contracts
Assets, Unobservable Input Reconciliation:
Opening Balance	14,389	8,177
Total realized and unrealized gains (losses) included in Net income	7,632	14,389
Issuances	0	0
Settlements	(14,389)	(8,177)
Closing Balance	7,632	14,389
Unrealized gains (losses) outstanding, at end of period	7,632	14,389
Liabilities, Unobservable Input Reconciliation:
Opening Balance	13,537	9,208
Total realized and unrealized gains (losses) included in Net income	14,971	13,537
Issuances		0
Settlements	(13,537)	(9,208)
Closing Balance	14,971	13,537
Unrealized (gains) losses outstanding, at end of period	14,971	13,537
Nasdaq Forwards
Assets, Unobservable Input Reconciliation:
Opening Balance	26,502	77,619
Total realized and unrealized gains (losses) included in Net income	(13,680)	(51,117)
Issuances	0	0
Settlements	0	0
Closing Balance	12,822	26,502
Unrealized gains (losses) outstanding, at end of period	$ 12,822	$ 26,502