Commitments & Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Operating lease expiration period	2025-12
Rent expense	$ 19,379,000	$ 16,382,000	$ 13,516,000
Minimum rental payments under capital leases	512,000
Minimum rental payments under operating leases	60,554,000
Minimal rental payments under operating leases, net of sublease payments	419,000
Unconditional purchase obligations over next six years	$ 51,159,000
Minimum
Long-term Purchase Commitment [Line Items]
Operating lease term	1 year
Unconditional purchase obligations	1 year
Maximum
Long-term Purchase Commitment [Line Items]
Operating lease term	10 years
Unconditional purchase obligations	4 years