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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Class A Common Stock	Dec. 31, 2011 Class A Common Stock	Dec. 31, 2010 Class A Common Stock	Dec. 31, 2012 Class B Common Stock	Dec. 31, 2011 Class B Common Stock	Dec. 31, 2010 Class B Common Stock	Dec. 31, 2012 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2011 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2010 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2009 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2012 Range of Purchase Prices $10.51-$19.87 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2012 Range of Purchase Prices $25.15-$25.15 Management Stock Purchase Plan Restricted stock units (RSUs)	Dec. 31, 2012 Range of Purchase Prices $26.51-$26.51 Management Stock Purchase Plan Restricted stock units (RSUs)
Information about RSUs outstanding
Low end of purchase price range (in dollars per share)																						$ 10.51	$ 25.15	$ 26.51
High end of purchase price range (in dollars per share)																						$ 19.87	$ 25.15	$ 26.51
RSUs Outstanding
Number Outstanding (in shares)																		196	392	361	350	86	55	55
Weighted Average Purchase Price (in dollars per share)																		$ 22.88	$ 18.74	$ 16.92	$ 18.13	$ 19.14	$ 25.15	$ 26.51
RSUs Vested
Number Vested (in shares)																		81	157	105		61	20
Weighted Average Purchase Price (in dollars per share)																		$ 20.36	$ 15.57	$ 15.21		$ 18.84	$ 25.15
Dividends per common share (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