Leases - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended
	Dec. 31, 2007 USD ($) Building	Mar. 31, 2019 USD ($) Building RenewalOption	Dec. 31, 2018 USD ($)	May 31, 2018 USD ($) ft²	Jun. 30, 2017 USD ($)	Dec. 31, 2008 USD ($)
Leases [Line Items]
Sale of facility and associated real property	$ 109,000
Mortgage debt retired	47,700
Cash received net of transaction costs and debt retirement	$ 61,000
Net deferred gain on real estate sale			$ 8,000			$ 39,100
Leaseback transaction lease period	12 years
Number of building leased | Building	2	1
Number of vacated buildings | Building		1
Letter of credit					$ 3,000
Number of times to renew the lease contract | RenewalOption		2
Lease extension period		10 years
Lease description		At commencement of the lease, we were not reasonably certain to exercise either of the two 10-year extension options contained within the lease.
Operating lease cost		$ 1,900
Cash paid for cashflows from operating lease		1,600
Operating lease right of use asset		49,304	$ 0
Operating lease, liability		$ 70,414
Operating lease, weighted average remaining lease term		10 years 6 months 25 days
Operating lease, weighted average discount rate, percent		6.65%
Amended Lease Term
Leases [Line Items]
Lease expiration date		Dec. 31, 2029
Tenant improvement allowances					$ 13,100
Lease Agreement
Leases [Line Items]
Tenant improvement allowances				$ 4,200
Office space area leased | ft²				44,718
Lease term				10 years 10 months
Lease Agreement | Letter of Credit
Leases [Line Items]
Lease security deposit				$ 1,000