Stockholders' Equity - Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	6 Months Ended	12 Months Ended
Dec. 31, 2017	Jun. 30, 2019	Dec. 31, 2018
Equity [Abstract]
Value of shares repurchased during period	$ 8.0	$ 5.2	$ 25.9
Weighted average number of shares of common stock outstanding (as a percentage)	5.00%
Shares repurchased during period (in shares)		0.7	3.3
Average price per share (in dollars per share)		$ 7.10	$ 7.91
Share repurchase program, unfulfilled requests (in shares)		12.0
Share repurchase program, unfulfilled requests		$ 85.0
Stock repurchase program, unfilled requests, value per share (in dollars per share)		$ 7.10

Shares Outstanding, Weighted Average Number of Shares, Percentage

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Stock Repurchase Program, Unfulfilled Requests

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Stock Repurchase Program, Unfulfilled Requests, Shares

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Stock Repurchase Program, Unfulfilled Requests, Value Per Share

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Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

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Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

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-Name Accounting Standards Codification
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Total cost of shares repurchased divided by the total number of shares repurchased.

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