Leases, User Charges and Commitments - Summary of Other Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018
Leases [Abstract]
Operating cash flows from operating leases	$ 2,342	$ 4,716
Financing cash flows from finance leases	725	1,465	$ 1,483
Operating cash flows from finance leases	66	140
Cash paid for lease liabilities	3,133	6,321
Right-of-use assets obtained in exchange for new financing lease liabilities		6
Rights-of-use assets obtained in exchange for new operating lease liabilities	$ 3,686	$ 4,988