Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amount [Abstract]
Dividends paid to shareholders	$ 14,947	$ 14,943	$ 14,886
Cash dividends paid (in dollars per share)	$ 1.00	$ 1.00	$ 1.00
Additional Paid-in Capital [Member]
Amount [Abstract]
Balance, Beginning period	50,594	50,275	48,751
Restricted stock grant	1,260	319	1,524
Balance, Period end	51,854	50,594	50,275
Class A [Member]
Shares [Abstract]
Balance, Beginning period (in shares)	2,623,109	2,623,109	2,623,109
Restricted stock grant (in shares)	0	0	0
Balance, Period end (in shares)	2,623,109	2,623,109	2,623,109
Amount [Abstract]
Balance, Beginning period	112	112	112
Restricted stock grant	0	0	0
Balance, Period end	112	112	112
Stated value of common stock (in dollars per share)	$ 0.04
Class B [Member]
Shares [Abstract]
Balance, Beginning period (in shares)	12,304,191	12,290,035	12,225,348
Restricted stock grant (in shares)	52,198	14,156	64,687
Balance, Period end (in shares)	12,356,389	12,304,191	12,290,035
Amount [Abstract]
Balance, Beginning period	525	524	522
Restricted stock grant	2	1	2
Balance, Period end	$ 527	$ 525	$ 524
Stated value of common stock (in dollars per share)	$ 0.04