Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies [Abstract]
Total rental expense under operating leases	$ 29,039	$ 27,431	$ 27,210
Future minimum lease payments for operating leases [Abstract]
2018	19,773
2019	14,360
2020	11,082
2021	8,499
2022	6,634
Thereafter	20,478
Environmental Matters
Accrued environmental liabilities	13,307
Accrued environmental liabilities, current	4,727
Accrued environmental liabilities, noncurrent	8,580
Estimated purchase commitments [Abstract]
2018	41,166
2019	$ 15,758