Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total USD ($)	Treasury Stock USD ($)	Paid-in-Capital USD ($)	Retained Earnings USD ($)	Accumulated Other Comprehensive Income/(Loss) USD ($)	Class A Common Stock	Class A Common Stock Common Stock USD ($)	Class B Common Stock Common Stock USD ($)
Balance at Dec. 31, 2011	$ 978,462	$ (65,048)	$ 741,848	$ 298,831	$ 2,724		$ 105	$ 2
Balance (in shares) at Dec. 31, 2011							102,985	2,060
Increase (Decrease) in Stockholders' Equity
Comprehensive income	64,211			63,857	354
Conversion of Class B stock to Class A stock							2	(2)
Conversion of Class B stock to Class A stock (in shares)							2,060	(2,060)
Repurchase of treasury stock	(4,748)	(4,748)
Repurchase of treasury stock (in shares)							(165)
Common stock dividends	(11,724)			(11,724)
Conversions to common stock	32,242		32,240				2
Conversions to common stock (in shares)							2,183
Non-cash stock-based compensation	1,176		1,176
Other	(1,051)			(1,051)
Balance at Mar. 31, 2012	1,058,568	(69,796)	775,264	349,913	3,078		109
Balance (in shares) at Mar. 31, 2012							107,063
Balance at Dec. 31, 2012	882,039	(423,900)	810,094	492,687	3,047		111
Balance (in shares) at Dec. 31, 2012						99,244	99,244
Increase (Decrease) in Stockholders' Equity
Comprehensive income	72,046			72,643	(597)
Repurchase of treasury stock	(61,310)	(61,310)
Repurchase of treasury stock (in shares)							(1,504)
Common stock dividends	(14,760)			(14,760)
Conversions to common stock	9,055		9,055
Conversions to common stock (in shares)							450
Non-cash stock-based compensation	1,815		1,815
Balance at Mar. 31, 2013	$ 888,885	$ (485,210)	$ 820,964	$ 550,570	$ 2,450		$ 111
Balance (in shares) at Mar. 31, 2013						98,190	98,190