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 (loss)	193,379			192,757	622
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	(358,852)	(358,852)
Repurchase of treasury stock (in shares)							(9,477)
Common stock dividends	(34,300)			(34,300)
Conversions to common stock	57,250		57,246				4
Conversions to common stock (in shares)							3,505
Non-cash stock-based compensation	3,609		3,609
Other	(1,051)			(1,051)
Balance at Sep. 30, 2012	838,497	(423,900)	802,703	456,237	3,346		111
Balance (in shares) at Sep. 30, 2012							99,073
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 (loss)	216,486			217,364	(878)
Repurchase of treasury stock	(238,406)	(238,406)
Repurchase of treasury stock (in shares)							(5,328)
Common stock dividends	(43,344)			(43,344)
Conversions to common stock	21,245		21,244				1
Conversions to common stock (in shares)							959
Non-cash stock-based compensation	5,861		5,861
Balance at Sep. 30, 2013	$ 843,881	$ (662,306)	$ 837,199	$ 666,707	$ 2,169		$ 112
Balance (in shares) at Sep. 30, 2013						94,875	94,875