Leases, User Charges and Commitments - Schedule of Future Minimum Lease Payments Under Operating and Finance Leases (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Operating Leases Liability, Less Than 1 year	$ 9,494
Operating Leases Liability, 1 - 3 years	14,576
Operating Leases Liability, 3 - 5 years	7,790
Operating Leases Liability, Over 5 years	5,156
Operating Leases Liability, Minimum lease payments	37,016
Operating Leases Liability, Imputed interest	3,197
Operating Leases Liability, Present value of minimum lease payments	33,819
Less: Operating Leases Liability, Current lease liabilities	8,468
Operating Leases Liability, Long-term lease liabilities	25,351
Finance Lease Liability, Less Than 1 Year	3,199
Finance Lease Liability, 1 - 3 Years	3,458
Finance Lease Liability, 3 - 5 years	4
Finance Leases Liability, Minimum lease payments	6,661
Finance Leases Liability, Imputed interest	273
Finance Leases Liability, Present value of minimum lease payments	6,388
Less: Finance Leases Liability, current lease liabilities	3,004	$ 2,845
Finance Leases Liability, Long-term lease liabilities	$ 3,384	$ 4,739