Fair Value of Financial Assets and Liabilities - Changes in Level 3 Nasdaq Forwards, Rate Lock Commitments, Forwards and Contingent Consideration Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets, Opening Balance	$ 73,448	$ 49,975	$ 92,528	$ 6,676
Assets, Total realized and unrealized gains (losses) included in Net income	20,044	33,061	(8,923)	33,061
Assets, Issuances		58,617		58,617
Assets, Settlements	(24,796)	(30,890)	(14,909)	(6,676)
Assets, Closing Balance	68,696	110,763	68,696	110,763
Assets, Unrealized gains (losses) outstanding	20,044	33,061	68,696	33,061
Liabilities, Opening Balance	68,401	36,159	49,230	26,758
Liabilities, Total realized and unrealized gains (losses) included in Net income	28,661	12,397	29,126	12,826
Liabilities, Issuances	1,180	10,006	8,937	10,695
Liabilities, Settlements	(31,022)	(14,831)	(20,073)	(6,548)
Liabilities, Closing Balance	67,220	43,731	67,220	43,731
Liabilities, Unrealized gains (losses) outstanding	28,661	12,397	29,126	12,826
Rate Lock Commitments [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets, Opening Balance	21,951	14,448	6,732	2,923
Assets, Total realized and unrealized gains (losses) included in Net income	26,691	6,219	26,691	6,219
Assets, Settlements	(21,951)	(14,448)	(6,732)	(2,923)
Assets, Closing Balance	26,691	6,219	26,691	6,219
Assets, Unrealized gains (losses) outstanding	26,691	6,219	26,691	6,219
Liabilities, Opening Balance	2,428	13,945	7,470	2,390
Liabilities, Total realized and unrealized gains (losses) included in Net income	1,198	12,089	1,198	12,089
Liabilities, Settlements	(2,428)	(13,945)	(7,470)	(2,390)
Liabilities, Closing Balance	1,198	12,089	1,198	12,089
Liabilities, Unrealized gains (losses) outstanding	1,198	12,089	1,198	12,089
Forward Sale Contracts [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets, Opening Balance	2,845	16,442	8,177	3,753
Assets, Total realized and unrealized gains (losses) included in Net income	1,567	20,515	1,567	20,515
Assets, Settlements	(2,845)	(16,442)	(8,177)	(3,753)
Assets, Closing Balance	1,567	20,515	1,567	20,515
Assets, Unrealized gains (losses) outstanding	1,567	20,515	1,567	20,515
Liabilities, Opening Balance	27,261	641	9,208	657
Liabilities, Total realized and unrealized gains (losses) included in Net income	25,971	37	25,971	37
Liabilities, Settlements	(27,261)	(641)	(9,208)	(657)
Liabilities, Closing Balance	25,971	37	25,971	37
Liabilities, Unrealized gains (losses) outstanding	25,971	37	25,971	37
Forward Contracts [Member] | NASDAQ [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Assets, Opening Balance	48,652	19,085	77,619
Assets, Total realized and unrealized gains (losses) included in Net income	(8,214)	6,327	(37,181)	6,327
Assets, Issuances		58,617		58,617
Assets, Closing Balance	40,438	84,029	40,438	84,029
Assets, Unrealized gains (losses) outstanding	(8,214)	6,327	40,438	6,327
Contingent Consideration [Member] | Accounts Payable, Accrued and Other Liabilities [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Liabilities, Opening Balance	38,712	21,573	32,552	23,711
Liabilities, Total realized and unrealized gains (losses) included in Net income	1,492	271	1,957	700
Liabilities, Issuances	1,180	10,006	8,937	10,695
Liabilities, Settlements	(1,333)	(245)	(3,395)	(3,501)
Liabilities, Closing Balance	40,051	31,605	40,051	31,605
Liabilities, Unrealized gains (losses) outstanding	$ 1,492	$ 271	$ 1,957	$ 700