Stockholders' Equity Dividends (Details) - $ / shares	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 1.316	$ 0.292	$ 1.608	$ 0.564
July 2017 dividend payment [Member]
Class of Stock [Line Items]
Dividends Payable, Date Declared, Month and Year			May 24, 2017
Dividends Payable, Date of Record			Jun. 05, 2017
Dividends Payable, Date to be Paid			Jul. 03, 2017
Common Stock, Dividends, Per Share, Declared			$ 0.146
October 2017 dividend payment [Member]
Class of Stock [Line Items]
Dividends Payable, Date Declared, Month and Year			Jul. 27, 2017
Dividends Payable, Date of Record			Sep. 07, 2017
Dividends Payable, Date to be Paid			Oct. 02, 2017
Common Stock, Dividends, Per Share, Declared			$ 0.146
January 2018 dividend payment [Member]
Class of Stock [Line Items]
Dividends Payable, Date Declared, Month and Year			Nov. 16, 2017
Dividends Payable, Date of Record			Dec. 07, 2017
Dividends Payable, Date to be Paid			Jan. 02, 2018
Common Stock, Dividends, Per Share, Declared			$ 0.158
April 2018 dividend payment [Member]
Class of Stock [Line Items]
Dividends Payable, Date Declared, Month and Year			Jan. 23, 2018
Dividends Payable, Date of Record			Mar. 05, 2018
Dividends Payable, Date to be Paid			Apr. 02, 2018
Common Stock, Dividends, Per Share, Declared			$ 0.158
April 2018 special dividend payment [Member]
Class of Stock [Line Items]
Dividends Payable, Date Declared, Month and Year			Jan. 23, 2018
Dividends Payable, Date of Record			Apr. 02, 2018
Dividends Payable, Date to be Paid			Apr. 23, 2018
Common Stock, Dividends, Per Share, Declared			$ 1