Statements of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Common Class A Common Stock	Common Class B Common Stock
Balances, beginning of period at Dec. 31, 2009	$ 703,259	$ 89,068	$ 674,115	$ (60,372)	$ 430	$ 18
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	4,402	4,398			4
Increase (Decrease) in Shareholders' Equity
Issuance of stock	224,313	224,233			80
Stock based compensation expense	9,386	9,386
Income tax effect of stock option exercises	284	284
Dividends	(16,181)		(16,181)
Net earnings (loss)	82,524		82,524
Amortization of accumulated other comprehensive loss related to de-designated hedges, net of income taxes	16,566			16,566
Balances, end of period at Dec. 31, 2010	1,024,553	327,369	740,458	(43,806)	514	18
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	10,113	10,106			7
Increase (Decrease) in Shareholders' Equity
Stock based compensation expense	9,636	9,636
Income tax effect of stock option exercises	3,047	3,047
Dividends	(16,846)		(16,846)
Net earnings (loss)	(228,063)		(228,063)
Amortization of accumulated other comprehensive loss related to de-designated hedges, net of income taxes	38,289			38,289
Balances, end of period at Dec. 31, 2011	840,729	350,158	495,549	(5,517)	521	18
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures	3,687	3,684			3
Increase (Decrease) in Shareholders' Equity
Stock based compensation expense	9,819	9,819
Income tax effect of stock option exercises	1,049	1,049
Dividends	(17,549)		(17,549)
Net earnings (loss)	171,539		171,539
Amortization of accumulated other comprehensive loss related to de-designated hedges, net of income taxes	5,517			5,517
Balances, end of period at Dec. 31, 2012	$ 1,014,791	$ 364,710	$ 649,539	$ 0	$ 524	$ 18