Shareholders' Equity - Dividends (Details) (USD $)	0 Months Ended		3 Months Ended																	12 Months Ended					0 Months Ended
	Feb. 05, 2014	Feb. 07, 2013	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Feb. 04, 2015
Class of Stock [Line Items]
Dividends (in dollars per share)			$ 0.11	[1]	$ 0.11	[1]	$ 0.11	[1]	$ 0.11	[1]	$ 0.10	[1]	$ 0.10	[1]	$ 0.10	[1]	$ 0.10	[1]	$ 0.09	$ 0.44	[1]	$ 0.40	[1]	$ 0.36
Increase in common stock dividend (as a percent)	10.00%	11.00%
Subsequent Event [Member]
Class of Stock [Line Items]
Dividends (in dollars per share)																									$ 0.12
Increase in common stock dividend (as a percent)																									9.00%

[1] Per share amounts for the quarters and the full years have each been calculated separately. Accordingly, quarterly amounts may not sum up to the annual amounts because of differences in the average common shares outstanding during each period and, with regard to diluted per share amounts only, because of the inclusion of the effect of potentially dilutive securities only in the periods in which such effect would have been dilutive.