Stockholders' Equity (Schedule of Dividend Increases) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended
	Jul. 16, 2018	Apr. 30, 2018	Apr. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, dividends, rate increase, percent		17.00%	28.00%
Quarterly Common Stock Cash Dividend		$ 0.54	$ 0.46
Annual Common Stock Cash Dividend		$ 2.16	$ 1.84
Series A common stock, $0.0001 par value, 400,000,000 shares authorized (2018: 168,294,244 issued and 135,018,148 outstanding; 2017: 168,156,969 issued and 135,769,256 outstanding)
Stockholders' Equity Note [Abstract]
Common Stock, Shares, Outstanding				135,018,148	135,769,256
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share				$ 0.0001	$ 0.0001
Common Stock, Shares Authorized				400,000,000	400,000,000
Common Stock, Shares, Issued				168,294,244	168,156,969
Series B common stock, $0.0001 par value, 100,000,000 shares authorized (2018 and 2017: 0 issued and outstanding)
Stockholders' Equity Note [Abstract]
Common Stock, Shares, Outstanding				0	0
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share				$ 0.0001	$ 0.0001
Common Stock, Shares Authorized				100,000,000	100,000,000
Common Stock, Shares, Issued				0	0
Subsequent Event [Member]
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.54
Dividends, Common Stock, Cash	$ 73