Fair Value Measurements and Derivative Instruments (Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	$ 885,413	$ 667,638
Total liabilities	(4,123)	(1,402)
Money market funds
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	508,019	401,805
Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	26,583	21,979
Commingled fixed income securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	21,391	20,060
Government and related securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	33,533	82,050
Corporate debt securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	71,433	72,149
Mortgage-backed / asset-backed securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	220,678	66,339
Foreign exchange contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	3,776	3,256
Total liabilities	(1,960)	(1,402)
Interest rate swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total liabilities	(2,163)
Level 1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	91,726	227,669
Total liabilities	0	0
Level 1 | Money market funds
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	73,228	161,441
Level 1 | Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 1 | Commingled fixed income securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	1,722	1,656
Level 1 | Government and related securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	16,776	64,572
Level 1 | Corporate debt securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 1 | Mortgage-backed / asset-backed securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 1 | Foreign exchange contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Total liabilities	0	0
Level 1 | Interest rate swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total liabilities	0
Level 2
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	793,687	439,969
Total liabilities	(4,123)	(1,402)
Level 2 | Money market funds
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	434,791	240,364
Level 2 | Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	26,583	21,979
Level 2 | Commingled fixed income securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	19,669	18,404
Level 2 | Government and related securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	16,757	17,478
Level 2 | Corporate debt securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	71,433	72,149
Level 2 | Mortgage-backed / asset-backed securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	220,678	66,339
Level 2 | Foreign exchange contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	3,776	3,256
Total liabilities	(1,960)	(1,402)
Level 2 | Interest rate swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total liabilities	(2,163)
Level 3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Total liabilities	0	0
Level 3 | Money market funds
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Equity securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Commingled fixed income securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Government and related securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Corporate debt securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Mortgage-backed / asset-backed securities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Level 3 | Foreign exchange contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total assets	0	0
Total liabilities	0	$ 0
Level 3 | Interest rate swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total liabilities	$ 0