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Preferred and Common Stockholder's Equity - Additional Information (Detail) - USD ($) | 6 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2016
Class of Stock [Line Items] |  |  |  |
Preferred stock, shares authorized | 5,000,000 |  |  |
Preferred stock, par value | $ 0.01 |  |  |
Preferred stock, shares outstanding | 0 |  |  |
Common stock, shares authorized | 150,000,000 |  |  |
Common stock, par value | $ 0.01 |  |  |
Common stock, shares issued | 73,200,000 | 70,600,000 | 68,400,000 |
Common stock, shares outstanding | 73,200,000 | 70,600,000 | 68,400,000 |
Share repurchase program, remaining authorized repurchase amount | $ 110,700,000 |  |  |
Payments for repurchase of company stock | $ 50,000,000 |  |  |
Eighth Share Repurchase Program [Member] |  |  |  |
Class of Stock [Line Items] |  |  |  |
Share repurchase program, authorized amount |  |  |  | $ 200,000,000

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