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Equity (Stock Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Stock repurchased and retired during period, shares		0.8	0.0		0.0	10.2
Common stock value acquired including acquisition costs		$ 8,300,000				$ 98,400,000
Average cost per share	$ 11.51	$ 10.22				$ 9.67
Repurchase of common stock, authorized amount			$ 41,700,000.0	$ 41,700,000.0
Class of Stock [Line Items]
Shares repurchased (in shares)	4.0
Repurchase of stock	$ 45,900,000			$ 8,304,000	$ 45,928,000	$ 98,429,000
3.125% senior convertible notes
Class of Stock [Line Items]
Stated interest rate (percent)	3.125%		3.125%	3.125%

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Common Stock Acquired, Average Cost Per Share

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Common Stock Value Acquired Including Acquisition Costs

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of stock repurchase plan authorized.

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Number of shares that have been repurchased and retired during the period.

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