Equity (Details) (USD $)	1 Months Ended			12 Months Ended
	Feb. 28, 2014	Jul. 31, 2013	Feb. 28, 2013	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011	May 16, 2012	May 31, 2005
Common Stock
Common stock quarterly dividend per share, after increase (in dollars per share)	$ 0.35	$ 0.33	$ 0.30	$ 1.26	$ 0.80	$ 0.48
Common stock quarterly dividend per share, before increase (in dollars per share)			$ 0.25
Number of common stock share authorized before amendment to Restated Articles of Incorporation							100,000,000
Number of common stock shares authorized				200,000,000	200,000,000		200,000,000
Common stock, par value (in dollars per share)
Votes per share of common stock				1
Share Repurchase Program
Number of shares authorized by the Board of Directors to be repurchased under stock repurchase program								12,000,000
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares)				7,883,033
Number of shares repurchased under stock repurchase program				0	0	0
Preferred Stock
Preferred stock, authorized shares				5,000,000	5,000,000
Preferred stock, par value (in dollars per share)
Preferred stock, issued shares				0	0
Preferred stock, outstanding shares				0	0
Minimum number of series in which preferred shares may be issued				1