Equity - Reincorporation, Common Stock (Details)	1 Months Ended				12 Months Ended
	Feb. 28, 2017 $ / shares	Jul. 31, 2016 $ / shares	Feb. 28, 2015 $ / shares	Feb. 28, 2014 $ / shares	Dec. 31, 2016 item $ / shares shares	Dec. 31, 2015 $ / shares shares	Dec. 31, 2014 $ / shares
Common Stock
Number of common stock shares authorized | shares					200,000,000	200,000,000
Preferred stock, par value (in dollars per share)					$ 0.001	$ 0.001
Common stock, par value (in dollars per share)					$ 0.001	0.001
The number of consecutive years the company has paid regular common stock quarterly dividends. | item					57
Votes per share of common stock | item					1
Common stock quarterly dividend per share (in dollars per share)	$ 0.45	$ 0.425	$ 0.40	$ 0.35	$ 1.65	$ 1.60	$ 1.40
Common stock quarterly dividend per share, before increase (in dollars per share)				$ 0.33