Fair Value of Financial Assets and Liabilities - Roll forward of Derivative Instruments and Contingent Consideration Require Valuation Based upon Significant Unobservable Inputs (Detail) - Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Opening Balance	$ 27,340	$ 48,967
Total realized and unrealized (gains) losses included in Net income	7,170	2,900
Settlements	(4,387)	(20,407)
Closing Balance	30,123	31,460
Unrealized (gains) losses outstanding	7,170	2,900
Contingent Consideration [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Opening Balance	23,711	38,713
Total realized and unrealized (gains) losses included in Net income	134	438
Settlements	(758)	(10,153)
Closing Balance	23,087	28,998
Unrealized (gains) losses outstanding	134	438
Rate Lock Commitments and Forwards, Net [Member]
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Opening Balance	3,629	10,254
Total realized and unrealized (gains) losses included in Net income	7,036	2,462
Settlements	(3,629)	(10,254)
Closing Balance	7,036	2,462
Unrealized (gains) losses outstanding	$ 7,036	$ 2,462