Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowances	$ 31,389	$ 48,138
Accumulated depreciation	$ 91,806	$ 88,603
Series A preferred shares outstanding (shares)	200,000	200,000
Series A preferred shares, liquidation preference	$ 203,000	$ 203,000
Preferred shares, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred shares authorized (shares)	4,000,000.0
Preferred shares outstanding (shares)	0	0
Common shares, par value (in dollars per share)	$ 0.001	$ 0.001
Common shares issued (shares)	94,800,000	93,900,000
Common shares outstanding (shares)	68,800,000	73,600,000
Treasury stock (shares)	26,000,000	20,300,000

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The aggregate liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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