Commitments and Contingencies - Additional Information (Detail) $ in Thousands		3 Months Ended
	Jan. 05, 2018 building	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Sale Leaseback Transaction [Line Items]
Proceeds from sale of Summers Ridge Property		$ 146,644	$ 0
Operating Leases, Rent Expense		6,000
Operating Leases, Future Minimum Payments Due, Next Twelve Months		6,200
Accrued in other current liabilities		14,062		$ 12,666
Operating Leases, Future Minimum Payments, Due in Two Years		6,400
Operating Leases, Future Minimum Payments, Due in Three Years		6,600
Operating Leases, Future Minimum Payments, Due in Four Years		6,800
Operating Leases, Future Minimum Payments, Due in Five Years		7,000
Operating Leases, Future Minimum Payments, Due Thereafter		$ 73,000
Sale Leaseback Transaction, Lease Terms	P15Y
Sale Leaseback Transaction, Number Of Buildings | building	2