Statements Of Changes In Shareholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Capital In Excess Of Par Value [Member]
Balance at Dec. 31, 2010	$ 668,649	$ 8,389	$ 574,030	$ 86,230
Balance, in shares at Dec. 31, 2010		83,891
Net income	139,470		139,470
Issuance and sale of common stock, shares		2,274
Stock Issued During Period, Value, New Issues	48,400	227		48,173
Balance at Dec. 31, 2011	856,519	8,616	713,500	134,403
Balance, in shares at Dec. 31, 2011		86,165
Net income	169,452		169,452
Adjustments to Additional Paid in Capital, Other	(2)			(2)
Balance at Dec. 31, 2012	1,025,969	8,616	882,952	134,401
Balance, in shares at Dec. 31, 2012		86,165
Net income	206,113		206,113
Balance at Dec. 31, 2013	$ 1,232,082	$ 8,616	$ 1,089,065	$ 134,401