Common Stock (Details) (USD $)	12 Months Ended			24 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
Class of Stock [Line Items]
Cost of common stock purchased and retired		$ 3,356,000	$ 6,644,000
Minimum percentage of outstanding common stock held by two shareholders (in hundredths)	10.00%
Minimum percentage of common stock needs to held by shareholders having more than ten percent of Class A common stock as per class B Protection clause (in hundredths)	10.00%
Number of days from trigger date to purchase Class B common shares	90 days
Percentage of common stock held by shareholder one (in hundredths)	23.50%
Percentage of common stock held by shareholder two (in hundredths)	11.00%
Percentage shareholding of class B considered as per class B Protection clause	below 10%
Common stock dividends declared	3,200,000	3,100,000	3,200,000
Class A [Member]
Class of Stock [Line Items]
Common stock purchased and retired (in shares)	0
Common stock repurchased during the period (in shares)			0
Number of shareholders with ownership in excess of ten percent	2
Common stock dividends declared each quarter (in dollars per share)	$ 0.06	$ 0.06	$ 0.06
Class B [Member]
Class of Stock [Line Items]
Authorized amount of repurchase of outstanding Class B common shares			10,000,000
Common stock purchased and retired (in shares)	0	547,366	368,723
Cost of common stock purchased and retired			$ 6,600,000	$ 10,000,000
Common stock repurchased during the period (in shares)			0
Common stock dividends declared each quarter (in dollars per share)	$ 0.07	$ 0.07	$ 0.07