Acquisition of the New Business - Purchase Price Allocations (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Nov. 02, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Assets
Goodwill		$ 72,518		$ 72,518		$ 66,316
Activated Carbon
Assets
Goodwill		42,100		42,100
Alternative Materials
Assets
Goodwill		18,400		18,400
Activated Carbon and Filter Aid Business (New Business)
Assets
Cash and cash equivalents	$ 3,826
Receivables	10,077
Inventories	20,439
Other current assets	1,215
Property, plant and equipment	67,697
Intangibles	37,248
Goodwill	45,410
Other assets	188
Total assets	186,100
Liabilities
Accounts payable and accrued liabilities	6,151
Payroll and benefits payable	3,315
Accrued income taxes	581
Deferred income taxes - long term	6,188
Accrued pension and other liabilities	11,207
Total liabilities	27,442
Net assets	158,658
Payments to acquire business
Cash paid for acquisition	158,658
Cash acquired	(3,826)
Net cash paid for acquisition	154,832
Step-up of inventory	2,100
Amortization of inventory step-up				600
Deductible goodwill for tax purposes		0		0
Contingent liabilities assumed
Contingent liabilities related to AROs	1,900
Activated Carbon and Filter Aid Business (New Business) | Selling, general and administrative expense
Acquisition costs
Acquisition-related integration and transaction costs incurred		700	$ 1,300	2,800	$ 2,900
Activated Carbon and Filter Aid Business (New Business) | Activated Carbon
Assets
Goodwill		27,700		27,700
Activated Carbon and Filter Aid Business (New Business) | Alternative Materials
Assets
Goodwill		$ 17,700		$ 17,700
Activated Carbon and Filter Aid Business (New Business) | Unpatented technology and know-how
Separately identifiable intangible assets
Finite-lived intangibles	$ 14,200
Weighted-average estimated useful life	20 years
Activated Carbon and Filter Aid Business (New Business) | Customer relationships
Separately identifiable intangible assets
Finite-lived intangibles	$ 15,700
Weighted-average estimated useful life	20 years
Activated Carbon and Filter Aid Business (New Business) | Trade names and trademarks
Separately identifiable intangible assets
Indefinite-lived intangible assets	$ 7,300