Financial Instruments Measured at Fair Value (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures
Equity Method Investment, Ownership Percentage		8.40%
Unrealized Gain on Securities			$ 4,204
Unrealized Loss on Securities		$ (239)		$ (13,854)
Fair Value, Measurements, Recurring [Member]
Fair Value Disclosures
Cash and Cash Equivalents	[1]	6,062	18,579
Equity investments	[2]	45,879	44,677
Interest Rate Cash Flow Hedge Asset at Fair Value		20,983
Interest Rate Cash Flow Hedge Liability at Fair Value			(11,574)
Foreign Currency Contract, Asset, Fair Value Disclosure		12,760	21,718
Total Fair Value Assets And Liabilities Measured On Recurring Basis		85,684	73,400
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Disclosures
Cash and Cash Equivalents	[1]	6,062	18,579
Equity investments	[2]	45,879	44,677
Interest Rate Cash Flow Hedge Asset at Fair Value		0
Interest Rate Cash Flow Hedge Liability at Fair Value			0
Foreign Currency Contract, Asset, Fair Value Disclosure		0	0
Total Fair Value Assets And Liabilities Measured On Recurring Basis		51,941	63,256
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Disclosures
Cash and Cash Equivalents		0	0
Equity investments		0	0
Interest Rate Cash Flow Hedge Asset at Fair Value		20,983
Interest Rate Cash Flow Hedge Liability at Fair Value			(11,574)
Foreign Currency Contract, Asset, Fair Value Disclosure		12,760	21,718
Total Fair Value Assets And Liabilities Measured On Recurring Basis		33,743	10,144
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Disclosures
Cash and Cash Equivalents		0	0
Equity investments		0	0
Interest Rate Cash Flow Hedge Asset at Fair Value		0
Interest Rate Cash Flow Hedge Liability at Fair Value			0
Foreign Currency Contract, Asset, Fair Value Disclosure		0	0
Total Fair Value Assets And Liabilities Measured On Recurring Basis		$ 0	$ 0

[1] Cash equivalents include highly liquid investments with an original maturity of less than three months.

[2] The company has an 8.4% equity ownership interest in Marubun Corporation and a portfolio of mutual funds with quoted market prices. During 2020, 2019, and 2018 the company recorded unrealized gains (losses) of $(239), $4,204, and $(13,854), respectively, on equity securities held at the end of each year.