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, 2019	Dec. 31, 2018
Assets, Unobservable Input Reconciliation:
Opening Balance	$ 92,528	$ 6,676
Total realized and unrealized gains (losses) included in Net income	(4,693)	33,911
Issuances	0	58,617
Settlements	(14,909)	(6,676)
Closing Balance	72,926	92,528
Unrealized gains (losses) outstanding, at end of period	72,926	33,911
Liabilities, Unobservable Input Reconciliation:
Opening Balance	49,229	26,758
Total realized and unrealized (gains) losses included in Net income	27,948	17,378
Issuances	14,957	12,615
Settlements	(21,301)	(7,522)
Closing Balance	70,833	49,229
Unrealized gains (losses) outstanding, at end of period	27,948	17,378
Rate lock commitments
Assets, Unobservable Input Reconciliation:
Opening Balance	6,732	2,923
Total realized and unrealized gains (losses) included in Net income	32,035	6,732
Issuances	0	0
Settlements	(6,732)	(2,923)
Closing Balance	32,035	6,732
Unrealized gains (losses) outstanding, at end of period	32,035	6,732
Liabilities, Unobservable Input Reconciliation:
Opening Balance	7,470	2,390
Total realized and unrealized (gains) losses included in Net income	12,124	7,470
Issuances	0	0
Settlements	(7,470)	(2,390)
Closing Balance	12,124	7,470
Unrealized gains (losses) outstanding, at end of period	12,124	7,470
Forward Sale Contracts
Assets, Unobservable Input Reconciliation:
Opening Balance	8,177	3,753
Total realized and unrealized gains (losses) included in Net income	14,389	8,177
Issuances	0	0
Settlements	(8,177)	(3,753)
Closing Balance	14,389	8,177
Unrealized gains (losses) outstanding, at end of period	14,389	8,177
Liabilities, Unobservable Input Reconciliation:
Opening Balance	9,208	657
Total realized and unrealized (gains) losses included in Net income	13,537	9,208
Issuances	0	0
Settlements	(9,208)	(657)
Closing Balance	13,537	9,208
Unrealized gains (losses) outstanding, at end of period	13,537	9,208
Nasdaq Forwards
Assets, Unobservable Input Reconciliation:
Opening Balance	77,619	0
Total realized and unrealized gains (losses) included in Net income	(51,117)	19,002
Issuances	0	58,617
Settlements	0	0
Closing Balance	26,502	77,619
Unrealized gains (losses) outstanding, at end of period	26,502	19,002
Contingent consideration
Liabilities, Unobservable Input Reconciliation:
Opening Balance	32,551	23,711
Total realized and unrealized (gains) losses included in Net income	2,287	700
Issuances	14,957	12,615
Settlements	(4,623)	(4,475)
Closing Balance	45,172	32,551
Unrealized gains (losses) outstanding, at end of period	$ 2,287	$ 700