Stock-Based Compensation (Details 5) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended													12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Class A	Dec. 31, 2010 Class A	Dec. 31, 2009 Class A	Dec. 31, 2011 Class B	Dec. 31, 2010 Class B	Dec. 31, 2009 Class B	Dec. 31, 2011 Management Stock Purchase Plan Restricted stock units (RSUs) Y	Dec. 31, 2010 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2009 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2008 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2011 Range of Purchase Prices $7.04-$10.56 Management Stock Purchase Plan	Dec. 31, 2011 Range of Purchase Prices $7.04-$10.56 Management Stock Purchase Plan Restricted stock units (RSUs) Y	Dec. 31, 2011 Range of Purchase Prices $10.57-$17.60 Management Stock Purchase Plan	Dec. 31, 2011 Range of Purchase Prices $10.57-$17.60 Management Stock Purchase Plan Restricted stock units (RSUs) Y	Dec. 31, 2011 Range of Purchase Prices $17.61-$21.11 Management Stock Purchase Plan	Dec. 31, 2011 Range of Purchase Prices $17.61-$21.11 Management Stock Purchase Plan Restricted stock units (RSUs) Y	Dec. 31, 2011 Range of Purchase Prices $21.12-$24.64 Management Stock Purchase Plan	Dec. 31, 2011 Range of Purchase Prices $21.12-$24.64 Management Stock Purchase Plan Restricted stock units (RSUs) Y	Dec. 31, 2011 Range of Purchase Prices $24.65-$25.73 Management Stock Purchase Plan	Dec. 31, 2011 Range of Purchase Prices $24.65-$25.73 Management Stock Purchase Plan Restricted stock units (RSUs) Y
Information about RSUs outstanding
Low end of purchase price range (in dollars per share)																						$ 7.04		$ 10.57		$ 17.61		$ 21.12		$ 24.65
High end of purchase price range (in dollars per share)																						$ 10.56		$ 17.60		$ 21.11		$ 24.64		$ 25.73
RSUs Outstanding
Number Outstanding (in shares)																		392	361	350	297		17		123		150		3		99
Weighted Average Remaining Contractual Life (in years)																		1.2					2.1		0.2		1.2		3.3		2.3
Weighted Average Purchase Price (in dollars per share)																		$ 18.74	$ 16.92	$ 18.13	$ 21.86		$ 10.38		$ 13.25		$ 19.86		$ 22.42		$ 25.17
RSUs Vested
Number Vested (in shares)																		157	105	131			17		82		51		3		4
Weighted Average Purchase Price (in dollars per share)																		$ 15.57	$ 15.21	$ 21.12			$ 10.38		$ 13.25		$ 19.84		$ 22.42		$ 25.73
Dividends distributed on the company's Common Stock (in dollars per share)	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.44	$ 0.44