Supplemental Cash Flow Disclosures - Non-Cash Investing and Financing Activities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Supplemental Cash Flow Disclosures Noncash Investing And Financing Activities [Abstract]
Capital property and equipment acquired on account, but not paid as of December 31	$ 15,457	$ 9,791	$ 10,268
Retirement Savings Plan	0	777	690
Performance Incentive Plan	1,127	1,027	1,594
Capital Lease Obligation	2,070	3,471	4,824
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 0	$ 0	$ 30,164