Fair Value Measurements and Derivative Instruments (Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	$ 326,426	$ 325,794
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	412,588	508,019
Equity securities	30,115	26,583
Mortgage-backed / asset-backed securities	206,520	220,678
Total assets	790,837	885,413
Liabilities	(1,722)	(4,123)
Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	49,696	73,228
Equity securities	0	0
Mortgage-backed / asset-backed securities	0	0
Total assets	77,454	91,726
Liabilities	0	0
Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	362,892	434,791
Equity securities	30,115	26,583
Mortgage-backed / asset-backed securities	206,520	220,678
Total assets	713,383	793,687
Liabilities	(1,722)	(4,123)
Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0	0
Equity securities	0	0
Mortgage-backed / asset-backed securities	0	0
Total assets	0	0
Liabilities	0	0
Interest rate swaps | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	445
Derivative liabilities		(2,163)
Interest rate swaps | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0
Derivative liabilities		0
Interest rate swaps | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	445
Derivative liabilities		(2,163)
Interest rate swaps | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0
Derivative liabilities		0
Foreign exchange contracts | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	438	3,776
Derivative liabilities	(1,722)	(1,960)
Foreign exchange contracts | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liabilities	0	0
Foreign exchange contracts | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	438	3,776
Derivative liabilities	(1,722)	(1,960)
Foreign exchange contracts | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset	0	0
Derivative liabilities	0	0
Commingled fixed income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	1,706	1,722
Commingled fixed income securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	21,031	21,391
Commingled fixed income securities | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	1,706	1,722
Commingled fixed income securities | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	19,325	19,669
Commingled fixed income securities | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	0
Government and related securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	50,526	31,961
Government and related securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	52,026	33,533
Government and related securities | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	26,052	16,776
Government and related securities | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	25,974	16,757
Government and related securities | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	0
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	67,674	71,433
Corporate debt securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	67,674	71,433
Corporate debt securities | Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	0
Corporate debt securities | Level 2 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	67,674	71,433
Corporate debt securities | Level 3 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	$ 0	$ 0