Adoption of ASC 842 - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Right-of-use assets			$ 15,330,000	$ 15,900,000
Lease obligations			15,470,000	$ 15,900,000
Operating lease term not yet commenced, amount			$ 10,800,000
Operating lease term not yet commenced			1 year
Expenses associated with operating lease agreements	$ 10,235,000	$ 9,813,000