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	130,302			130,528	(226)
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	(58,822)	(58,822)
Repurchase of treasury stock (in shares)							(1,665)
Common stock dividends	(23,409)			(23,409)
Conversions to common stock	47,103		47,100				3
Conversions to common stock (in shares)							2,938
Non-cash stock-based compensation	2,320		2,320
Other	(1,051)			(1,051)
Balance at Jun. 30, 2012	1,074,905	(123,870)	791,268	404,899	2,498		110
Balance (in shares) at Jun. 30, 2012							106,318
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	143,026			144,331	(1,305)
Repurchase of treasury stock	(181,310)	(181,310)
Repurchase of treasury stock (in shares)							(4,180)
Common stock dividends	(29,140)			(29,140)
Conversions to common stock	12,568		12,567				1
Conversions to common stock (in shares)							614
Non-cash stock-based compensation	3,874		3,874
Balance at Jun. 30, 2013	$ 831,057	$ (605,210)	$ 826,535	$ 607,878	$ 1,742		$ 112
Balance (in shares) at Jun. 30, 2013						95,678	95,678