Fair Value Measurements and Derivative Instruments (Assets and Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	$ 290,598	$ 325,794
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	335,649	508,019
Equity securities	29,898	26,583
Mortgage-backed / asset-backed securities	187,435	220,678
Total assets	676,776	885,413
Liabilities	(2,853)	(4,123)
Level 1 | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	84,772	73,228
Equity securities	0	0
Mortgage-backed / asset-backed securities	0	0
Total assets	96,323	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	250,877	434,791
Equity securities	29,898	26,583
Mortgage-backed / asset-backed securities	187,435	220,678
Total assets	580,453	793,687
Liabilities	(2,853)	(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	631
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	631
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	723	3,776
Derivative liabilities	(2,853)	(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	723	3,776
Derivative liabilities	(2,853)	(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	1,704	1,722
Commingled fixed income securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	20,981	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	1,704	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	19,277	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	35,026	31,961
Government and related securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	35,026	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	9,847	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	25,179	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	66,433	71,433
Corporate debt securities | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	66,433	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	66,433	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