Employee Benefit Plans (Plan Assets at Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity partnerships
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember
Hedge fund investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember
Employee Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	$ 71,940	$ 73,357	$ 63,109
Employee Pension Plans | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	58,253	56,952
Employee Pension Plans | Level 1 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	58,253	56,952
Employee Pension Plans | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	3,086	2,861
Employee Pension Plans | Level 2 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	3,086	2,861
Employee Pension Plans | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Level 3 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Fair Value, Inputs, Level 1, 2 and 3 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	61,339	59,813
Employee Pension Plans | Fair Value Measured at Net Asset Value Per Share | Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	10,601	13,544
Employee Pension Plans | Cash and cash equivalents | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	1,582	2,867
Employee Pension Plans | Cash and cash equivalents | Level 1 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	1,582	2,867
Employee Pension Plans | Cash and cash equivalents | Level 2 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Cash and cash equivalents | Level 3 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Fixed income funds | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	5,086	2,861
Employee Pension Plans | Fixed income funds | Level 1 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	2,000	0
Employee Pension Plans | Fixed income funds | Level 2 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	3,086	2,861
Employee Pension Plans | Fixed income funds | Level 3 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Mutual funds | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	54,671	54,085
Employee Pension Plans | Mutual funds | Level 1 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	54,671	54,085
Employee Pension Plans | Mutual funds | Level 2 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Mutual funds | Level 3 | Non-Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	0	0
Employee Pension Plans | Equity partnerships | Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	3,700	3,660
Employee Pension Plans | Hedge fund investments | Closely Held Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plans' assets	$ 6,901	$ 9,884