XML 83 R72.htm IDEA: XBRL DOCUMENT v3.19.2
Stock Transactions and Unit Redemptions - Additional Information (Details) - USD ($)
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Mar. 31, 2019
Aug. 01, 2018
Jun. 30, 2018
Mar. 31, 2018
Mar. 12, 2018
Dec. 31, 2017
Class Of Stock [Line Items]                      
Number of authorized classes of common stock 2   2 2              
Class A Common Stock [Member]                      
Class Of Stock [Line Items]                      
Common stock voting rights description       Each share of Class A common stock is entitled to one vote              
Common stock, shares authorized 1,000,000,000 1,000,000,000 1,000,000,000 1,000,000,000 1,000,000,000            
Common stock, par value $ 0.01 $ 0.01 $ 0.01 $ 0.01 $ 0.01            
Common stock, shares outstanding 156,679,527 156,916,336 156,679,527 156,679,527 156,916,336 157,422,916   138,921,533 138,921,533   138,593,787
Stock repurchased during period 1,600,000 50,000 1,613,032 1,613,032              
Stock repurchased during period, Value $ 13,900,000 $ 500,000                  
Share repurchase and redemption unit remaining authorized amount     $ 186,104 $ 185,618 $ 199,514            
Class A Common Stock [Member] | Limited Partnership Interests or Other Equity Interests in Subsidiaries [Member] | Affiliated Persons or Entities [Member]                      
Class Of Stock [Line Items]                      
Stock repurchases and redeemed or repurchases authorized amount                   $ 100,000,000.0  
Class A Common Stock [Member] | Maximum [Member] | Limited Partnership Interests or Other Equity Interests in Subsidiaries [Member] | Affiliated Persons or Entities [Member]                      
Class Of Stock [Line Items]                      
Stock repurchases and redeemed or repurchases authorized amount             $ 200,000,000.0        
Class B Common Stock [Member]                      
Class Of Stock [Line Items]                      
Common stock voting rights description       Each share of Class B common stock is entitled to 10 votes              
Common stock, shares authorized 500,000,000 500,000,000 500,000,000 500,000,000 500,000,000            
Common stock, par value $ 0.01 $ 0.01 $ 0.01 $ 0.01 $ 0.01            
Conversion of common stock       1              
Common stock conversion features       Each share of Class B common stock is entitled to 10 votes and is convertible at any time into one share of Class A common stock.              
Common stock, shares outstanding 21,285,533 21,285,533 21,285,533 21,285,533 21,285,533