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Equity and Dividends (Schedule of Quarterly Dividends Declared and Paid) (Details) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
First Quarter 2017 [Member]    
Dividends Payable [Line Items]    
Declaration date May 04, 2017  
Dividends per share $ 0.1700  
Record date May 23, 2017  
Total dividends $ 18,188  
Payment date Jun. 13, 2017  
First Quarter 2016 [Member]    
Dividends Payable [Line Items]    
Declaration date   May 09, 2016
Dividends per share   $ 0.1600
Record date   May 24, 2016
Total dividends   $ 17,022
Payment date   Jun. 14, 2016
Fourth Quarter 2016 [Member]    
Dividends Payable [Line Items]    
Declaration date Jan. 23, 2017  
Dividends per share $ 0.1700  
Record date Feb. 10, 2017  
Total dividends $ 18,160  
Payment date Mar. 03, 2017  
Fourth Quarter 2015 [Member]    
Dividends Payable [Line Items]    
Declaration date   Jan. 15, 2016
Dividends per share   $ 0.1600
Record date   Feb. 12, 2016
Total dividends   $ 17,154
Payment date   Mar. 04, 2016