Fair Value Measurements - Available-for-sale Pension Surplus (Details) - Fair Value, Measurements, Recurring $ in Thousands	Sep. 30, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	$ 9,327
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	6,911
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	2,416
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pension surplus investment	$ 0