Restricted Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended		12 Months Ended		0 Months Ended
	May 31, 2012	May 31, 2011	Mar. 31, 2013	Mar. 31, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2012 Restricted Stock Units (RSUs) [Member] Class B [Member] Outside Director [Member]	Dec. 31, 2011 Restricted Stock Units (RSUs) [Member] Class B [Member] Outside Director [Member]	Feb. 04, 2013 Restricted Stock Units (RSUs) [Member] Class B [Member] Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares distribution period from grant date			1 year
Total value of shares issued					$ 440	$ 440	$ 1,241
Shares issued (in shares)							52,389
Value of each share issued (in dollars per share)	$ 21.87	$ 22.50					$ 23.69
Summary of stock Issuances [Abstract]
Shares granted (in shares)	20,119	19,558
Vesting Date	May 08, 2013	May 10, 2012
Service Period	7/1/2012 - 6/30/2013	7/1/2011 - 6/30/2012
Period restricted stocks will vest ratably from date of grant				3 years