Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amount [Abstract]
Dividends paid to shareholders	$ 15,003	$ 14,947	$ 14,943
Cash dividends paid (in dollars per share)	$ 1.00	$ 1.00	$ 1.00
Additional Paid-in Capital [Member]
Amount [Abstract]
Balance, Beginning period	$ 51,854	$ 50,594	$ 50,275
Restricted stock grant	1,092	1,260	319
Balance, Period end	$ 52,946	$ 51,854	$ 50,594
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)	12,356,389	12,304,191	12,290,035
Restricted stock grant (in shares)	46,552	52,198	14,156
Balance, Period end (in shares)	12,402,941	12,356,389	12,304,191
Amount [Abstract]
Balance, Beginning period	$ 527	$ 525	$ 524
Restricted stock grant	2	2	1
Balance, Period end	$ 529	$ 527	$ 525
Stated value of common stock (in dollars per share)	$ 0.04