Acquisition of the New Business - Purchase Price Allocations (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended		11 Months Ended
	Nov. 02, 2016	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Assets
Goodwill			$ 76,058		$ 76,058	$ 66,316
Activated Carbon
Assets
Goodwill			44,500		44,500
Alternative Materials
Assets
Goodwill			19,500		19,500
Activated Carbon and Filter Aid Business (New Business)
Assets
Cash and cash equivalents	$ 3,826		3,826		3,826
Receivables	10,077		10,077		10,077
Inventories	20,895		18,123		18,123
Other current assets	1,171		1,528		1,528
Property, plant and equipment	67,697		66,976		66,976
Intangibles	37,248		37,797		37,797
Goodwill	42,844		47,057		47,057
Other assets	179		388		388
Total assets	183,937		185,772		185,772
Liabilities
Accounts payable and accrued liabilities	6,151		5,539		5,539
Payroll and benefits payable	4,360		3,315		3,315
Accrued income taxes	581		581		581
Deferred income taxes - long term	7,406		6,472		6,472
Accrued pension and other liabilities	8,014		11,206		11,206
Total liabilities	26,512		27,113		27,113
Net assets	157,425		158,659		158,659
Payments to acquire business
Cash paid for acquisition	157,425				158,659
Cash acquired	(3,826)				(3,826)
Net cash paid for acquisition	153,599				154,833
Cash paid for acquisition - Measurement Period Adjustments					1,234
Measurement Period Adjustments
Inventories					(2,772)
Other current assets					357
Property, plant, and equipment					(721)
Intangibles					549
Goodwill					4,213
Other assets					209
Total Assets					1,835
Accounts payable and accrued liabilities					(612)
Payroll and benefits payable					(1,045)
Deferred income taxes - long term					(934)
Accrued pension and other liabilities					3,192
Total liabilities					601
Net assets					1,234
Step-up of inventory	1,300
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		$ 600	2,800	$ 3,500
Activated Carbon and Filter Aid Business (New Business) | Activated Carbon
Assets
Goodwill			29,000		29,000
Measurement Period Adjustments
Goodwill			2,500
Activated Carbon and Filter Aid Business (New Business) | Alternative Materials
Assets
Goodwill			18,100		$ 18,100
Measurement Period Adjustments
Goodwill			$ 1,700
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	$ 16,300
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