Commitments and Contingencies (Environmental Matters) (Details) $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended	12 Months Ended
	Feb. 13, 2013 USD ($)	Dec. 31, 2016 USD ($) property	Dec. 31, 2012 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Environmetal Remediation Obligations [Line Items]
Accrued environmental liabilities		$ 9,625					$ 9,625	$ 2,531
Previously incurred costs							$ 0	$ 2,900	$ 3,100
Environmental Remediation, Number of Properties Excluded From Regulatory Requirements | property		3
Costs | Second joint venture partner of former owner / operator
Environmetal Remediation Obligations [Line Items]
Ownership responsibility for site investigation and remediation costs (as a percent)		37.50%					37.50%
Environmental and other matters | Sold parcel
Environmetal Remediation Obligations [Line Items]
Remediation cost, expected cost							$ 100
Environmental and other matters | Costs | Former Owner / Operator
Environmetal Remediation Obligations [Line Items]
Ownership responsibility for site investigation and remediation costs (as a percent)		75.00%					75.00%
Environmental remediation expense							$ 5,700
Environmental and other matters | Costs | HHEM and H&H
Environmetal Remediation Obligations [Line Items]
Ownership responsibility for site investigation and remediation costs (as a percent)		25.00%					25.00%
Environmental loss contingencies, payments							$ 1,000
Environmental remediation expense							$ 1,800
Scenario, forecast | Environmental and other matters | Sold parcel
Environmetal Remediation Obligations [Line Items]
Remediation cost, expected cost						$ 200
SL Industries, Inc. (SLI) | SurfTech Sites [Member]
Environmetal Remediation Obligations [Line Items]
Loss Contingency, Settlement Agreement, Amount Offered	$ 300
SL Industries, Inc. (SLI) | Scenario, forecast | SurfTech Sites [Member]
Environmetal Remediation Obligations [Line Items]
Remediation cost, expected cost				$ 1,400
Environmental loss contingencies, payments					$ 2,100
Unfavorable regulatory action | SurfTech Sites [Member]
Environmetal Remediation Obligations [Line Items]
Accrual for environmental loss contingencies			$ 1,800