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Subsequent Events - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Aug. 03, 2017
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Subsequent Event [Line Items]            
Dividends Payable, Date Declared   May 04, 2017 Feb. 24, 2017      
Dividends payment date   Jul. 31, 2017 Apr. 28, 2017      
Record date for dividends declared   Jun. 30, 2017 Mar. 31, 2017      
Dividends payable Per Share (in dollars per share)   $ 0.4180 $ 0.4138 $ 0.4180    
Cash paid for acquisition       $ 170,028 $ 0  
Equity Method Investments   $ 240,561   $ 240,561   $ 233,294
Subsequent Event [Member]            
Subsequent Event [Line Items]            
Dividends Payable, Date Declared Aug. 03, 2017          
Dividends payment date Oct. 31, 2017          
Record date for dividends declared Sep. 29, 2017          
Dividends payable Per Share (in dollars per share) $ 0.420          
Dividends annualized (in dollars per share) $ 1.68          
Increase in dividends payable percentage 0.50%