Pension and Other Postretirement Benefit Plans (Fair values of the plans assets) (Details) - Swiss Pension Plan - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		$ 43,428	$ 39,144	$ 39,002
Active Market Prices (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		25,269	21,028
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		1,152	1,082
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Cash held in Swiss Franc, Euro and USD
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		1,670	705
Cash held in Swiss Franc, Euro and USD | Active Market Prices (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		1,670	705
Cash held in Swiss Franc, Euro and USD | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Cash held in Swiss Franc, Euro and USD | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		15,487	12,534
Equity securities | Active Market Prices (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		14,364	11,481
Equity securities | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		1,123	1,053
Equity securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Fixed income / Bond securities:
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		9,235	8,842
Fixed income / Bond securities: | Active Market Prices (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		9,235	8,842
Fixed income / Bond securities: | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Fixed income / Bond securities: | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Other assets (accounts receivable, assets at real estate management company)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		29	29
Other assets (accounts receivable, assets at real estate management company) | Active Market Prices (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Other assets (accounts receivable, assets at real estate management company) | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		29	29
Other assets (accounts receivable, assets at real estate management company) | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan		0	0
Investments measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Net assets of pension plan	[1]	$ 17,007	$ 17,034

[1] Investments measured at net asset value represent real estate investment funds that are measured at fair value using the net asset value per share (or its equivalent) practical expedient and therefore have not been categorized in the fair value hierarchy. The fair value amounts presented in these tables are intended to permit reconciliation of the fair value hierarchy to the total plan assets disclosed above.