Lease Obligations - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Rent expense related to operating leases	$ 3,800,000	$ 3,600,000	$ 2,500,000
Operating Leases, Future Minimum Payments Due, Next Twelve Months	2,300,000
Operating Leases, Future Minimum Payments, Due in Two Years	1,998,000
Operating Leases, Future Minimum Payments, Due in Three Years	1,800,000
Operating Leases, Future Minimum Payments, Due in Four Years	1,689,000
Operating Leases, Future Minimum Payments, Due in Five Years	1,642,000
Future minimum payments under current lease agreements, thereafter	5,400,000
Future minimum payments under current lease agreements, total	14,800,000
Capital Leases, Future Minimum Payments Due, Next Twelve Months	2,400,000		$ 1,500,000
Capital Leases, Future Minimum Payments Due in Five Years	$ 1,315,000