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Stockholders' Equity - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dividends Payable [Line Items]            
Cash dividends declared per common share (usd per share)   $ 0.08 $ 0.07 $ 0.07 $ 0.15 $ 0.14
Payments of common stock dividends   $ 4.8 $ 4.2 $ 4.2 $ 9.0 $ 8.4
Subsequent Event            
Dividends Payable [Line Items]            
Cash dividends declared per common share (usd per share) $ 0.08