Note H - Employee Benefit Plans - Funded Pensions Assets by Assets Category (Details) - USD ($) $ in Thousands		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total plan assets		$ 129,348	$ 118,092
Total plan assets, percentage		100.00%	100.00%
Pension Plan [Member]
Total plan assets		$ 129,348	$ 118,092	$ 107,862
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Total plan assets		106,639	107,943
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Total plan assets		7,574	4,242
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Total plan assets
Equity Securities [Member]
Total plan assets		$ 79,906	$ 68,563
Total plan assets, percentage		62.00%	58.00%
Equity Securities [Member] | Pension Plan [Member]
Total plan assets		$ 79,906	$ 68,563
Equity Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Total plan assets		79,906	68,563
Equity Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Total plan assets
Equity Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Total plan assets
Debt Securities [Member]
Total plan assets		$ 34,307	$ 43,622
Total plan assets, percentage		26.00%	37.00%
Debt Securities [Member] | Pension Plan [Member]
Total plan assets		$ 34,307	$ 43,622
Debt Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Total plan assets		26,733	39,380
Debt Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Total plan assets		7,574	4,242
Debt Securities [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Total plan assets
Other than Securities Investment [Member]
Total plan assets		$ 15,135	$ 5,907
Total plan assets, percentage		12.00%	5.00%
Investments Excluding Investments at NAV [Member] | Pension Plan [Member]
Total plan assets		$ 114,213	$ 112,185
Investments Excluding Investments at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Total plan assets		106,639	107,943
Investments Excluding Investments at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Total plan assets		7,574	4,242
Investments Excluding Investments at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Total plan assets
Investment at NAV [Member] | Pension Plan [Member]
Total plan assets	[1]	15,135	5,907
Investment at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Total plan assets	[1]
Investment at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Total plan assets	[1]
Investment at NAV [Member] | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Total plan assets	[1]

[1] Investment valued at NAV are comprised of cash, cash equivalents, and short-term investments used to provide liquidity for the payment of benefits and other purposes. The commingled funds are valued at NAV based on the market value of the underlying investments, which are primarily government issued securities.