Stockholders' Equity - Narrative (Details) (USD $)	0 Months Ended		3 Months Ended				12 Months Ended				0 Months Ended
	Jul. 19, 2013	Sep. 28, 2012	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2006	Feb. 04, 2014 Subsequent Event [Member] Dividend Declared [Member]
Schedule of sale of stock under market equity offering Program
Shares Sold							5,207,871	0	11,648,700
Sales Price Per Share, minimum							$ 24.19	$ 0	$ 20.27
Sales Price Per Share, maximum							$ 30.49	$ 0	$ 23.63
Net Proceeds							$ 140,600,000	$ 0	$ 251,600,000
Number of Authorized Shares Remaining Under Offering Program			5,391,400				5,391,400
Stockholders Equity (Textual) [Abstract]
Issuance of common stock	3,000,000	9,200,000
Common Stock, Par or Stated Value Per Share			$ 0.01				$ 0.01	$ 0.01
Gross price per share		$ 23.87
Net price per share	$ 26.13	$ 22.85
Proceeds from issuance of common stock, net	78,300,000	201,100,000					220,252,000	202,352,000	251,916,000
Dividends per share to common stockholders, declared							$ 1.20				$ 0.30
Dividend per share to common stockholders, paid			$ 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							$ 2,100,000	$ 1,200,000