Fair Value Measurements (Available-for-sale Pension Surplus) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	$ 6,930	$ 9,106
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	5,072	6,706
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	1,858	2,400
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	$ 0	$ 0