Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 11,200	$ 12,300	$ 21,300	$ 22,600
Amortization expense on finance leases	$ 609		1,198
Property and equipment purchased through accounts payable and accrued liabilities, increased amount			$ 3,200	$ 100