Fair Value of Financial Assets and Liabilities - Quantitative Information about Level 3 Fair Value Measurements on Recurring Basis (Detail) $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Level 3 [Member] | Rate Lock Commitments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	$ 14,448	$ 2,923
Liabilities, fair value	13,945	2,390
Level 3 [Member] | Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets, fair value	16,442	3,753
Liabilities, fair value	$ 641	$ 657
Minimum [Member] | Measurement Input, Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	3.0	3.0
Maximum [Member] | Measurement Input, Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	13.5	13.5
Accounts Payable, Accrued and Other Liabilities [Member] | Contingent Consideration [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities, fair value	$ 53,164	$ 67,172
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Probability of meeting earnout and contingencies	97.00%	97.00%
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member] | Measurement Input, Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	8.1	8.2
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Probability of meeting earnout and contingencies	75.00%	75.00%
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member] | Minimum [Member] | Measurement Input, Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	3.3	3.3
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Probability of meeting earnout and contingencies	100.00%	100.00%
Accounts Payable, Accrued and Other Liabilities [Member] | Present Value of Expected Payments [Member] | Contingent Consideration [Member] | Maximum [Member] | Measurement Input, Discount Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Discount rate	10.4	10.4