Stock Options and Incentive Plans (Narrative) (Details) (USD $)	12 Months Ended									12 Months Ended			1 Months Ended		12 Months Ended					12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2007	Dec. 31, 2011 Prosperity Plus Savings Plan [Member]	Dec. 31, 2010 Prosperity Plus Savings Plan [Member]	Dec. 31, 2009 Prosperity Plus Savings Plan [Member]	Dec. 31, 2011 Prosperity Plus Savings Plan [Member] Minimum [Member]	Dec. 31, 2011 Prosperity Plus Savings Plan [Member] Maximum [Member]	Dec. 31, 2011 Profit Sharing Plan [Member]	Dec. 31, 2010 Profit Sharing Plan [Member]	Dec. 31, 2009 Profit Sharing Plan [Member]	Mar. 31, 2011 Long Term Incentive Plan [Member]	Mar. 31, 2010 Long Term Incentive Plan [Member]	Dec. 31, 2011 Long Term Incentive Plan [Member]	Dec. 31, 2010 Long Term Incentive Plan [Member]	Dec. 31, 2009 Long Term Incentive Plan [Member]	Dec. 31, 2011 Long Term Incentive Plan [Member] Minimum [Member]	Dec. 31, 2011 Long Term Incentive Plan [Member] Maximum [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	Dec. 31, 2009 Restricted Stock [Member]	Dec. 31, 2011 Additional Restricted Stock Plan [Member]	Dec. 31, 2010 Additional Restricted Stock Plan [Member]	Dec. 31, 2009 Additional Restricted Stock Plan [Member]	Dec. 31, 2011 Deferred Compensation [Member]	Dec. 31, 2010 Deferred Compensation [Member]	Dec. 31, 2009 Deferred Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense			$ 70,000
Contractual term of stock options, in years	20 years
Length of time options are valid after retirement, in years	10 years
Options granted				one option for 250,000 shares of Class A Common Stock
Minimum market price for options to be exercisable				$ 48.0
Incremental vesting percent	20.00%																						25.00%
Aggregate intrinsic value of vested options	2,800,000
Aggregate intrinsic value of options exercised	300,000
Term of payout (in years)																		1 year	3 years
Shares issued for long term incentive plan													32,177	22,844
Cash payments in connection with long term incentive plan													800,000	1,100,000
Compensation plan, cost															2,400,000	1,500,000	1,600,000			2,500,000	2,800,000	2,600,000	1,300,000	1,500,000	1,600,000
Vesting period															the vesting period, which includes the year for which performance targets are measured and the two subsequent years.
Deferred compensation	1,121,000	2,176,000
Employee contribution, percent								1.00%	15.00%
Percent of employee contribution matched by the Company								50.00%	100.00%
Maximum percent of annual compensation which the Company can match					5.00%
Deferred compensation, expense					$ 3,700,000	$ 3,700,000	$ 3,700,000			$ 2,300,000	$ 2,300,000	$ 1,600,000														$ 100,000	$ 200,000	$ 300,000