Accounts Payable and Accrued Liabilities - Carrying Value of Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accounts payable	$ 376,277	$ 258,203
Current deferred revenue	90,639	80,503
Wages, severance and related taxes	57,633	76,157
Accrued rebates	38,025	33,071
Employee benefits	25,406	24,395
Accrued interest	22,019	27,202
Other (individual items less than 5% of total current liabilities)	68,929	69,012
Accounts payable and accrued liabilities	$ 678,928	$ 568,543