Stockholders' Equity (Details 1) (USD $)	0 Months Ended	3 Months Ended				12 Months Ended				1 Months Ended	0 Months Ended
	Sep. 28, 2012	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2006	Jan. 31, 2013 Subsequent Event [Member]	Jan. 29, 2013 Subsequent Event [Member] Dividend Declared [Member]
Schedule of sale of stock under market equity offering Program
Shares Sold							11,648,700	5,258,700		1,599,271
Sales Price Per Share, minimum						$ 0	$ 20.27	$ 20.23
Sales Price Per Share, maximum						$ 0	$ 23.63	$ 25.16
Net Proceeds							$ 251,600,000	$ 117,700,000		$ 39,700,000
Stockholders Equity (Textual) [Abstract]
Issuance of stock	9,200,000
Gross price per share	$ 23.87
Net price per share	$ 22.85
Proceeds from issuance of common stock, net	201,100,000					202,352,000	251,916,000	118,205,000
Dividends per share to common stockholders						$ 1.20					$ 0.30
Dividend per share to common stockholders		$ 0.3	$ 0.3	$ 0.3	$ 0.30	$ 1.20	$ 1.20	$ 1.20
Number of common shares authorized to be repurchased									3,000,000
Other comprehensive income loss reduction in future benefit obligations related to pension plan						$ 1,200,000	$ 1,900,000