CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares issued (in shares)	0	0
Treasury stock (in shares)	14,592,888	14,592,888
Class A
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	75,714,163	71,727,061
Treasury stock (in shares)	14,592,888	14,592,888
Class B
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	20,308,454	23,793,669
Treasury stock (in shares)	0	0

Face amount or stated value per share of common stock.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29,30)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

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