Pension (Plan Asset Allocation, Fair Value) (Details) - Pension Plan - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 343,219		$ 318,414	$ 316,184
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 343,219		318,414	$ 316,184
Target allocation		100.00%
U.S. Plans | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Target allocation		3.00%
U.S. Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Target allocation		5.00%
U.S. Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation		45.00%
U.S. Plans | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation		37.00%
U.S. Plans | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Target allocation		10.00%
U.S. Plans | Level Two | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	$ 9,100
Measured at NAV as a practical expedient | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		343,219		318,414
Measured at NAV as a practical expedient | U.S. Plans | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		8,061		8,766
Measured at NAV as a practical expedient | U.S. Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		16,390		15,812
Measured at NAV as a practical expedient | U.S. Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		156,434		148,302
Measured at NAV as a practical expedient | U.S. Plans | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		125,671		96,658
Measured at NAV as a practical expedient | U.S. Plans | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 36,663	[1]	$ 48,876

[1] Includes $9.1 million of hedge funds valued daily at NAV which is considered to be a Level 2 investment in the fair value hierarchy. See note 14 for discussion of the fair value hierarchy.