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Stockholders' Equity Share Activity by Class (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(24,233)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	(126,971)	(82,729)	(77,442)
Outstanding	78,572,110	77,801,854	76,942,872	75,569,845
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	304,570	297,891	246,581
Class A Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(24,233)
Shares repurchased and retired during the period (shares)	(43,091)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	(126,971)	(82,729)	(77,442)
Outstanding	63,131,007	56,429,825	54,071,188	50,463,126
Class B Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(1,777,326)		(644,424)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	0	0	0
Outstanding	4,457,958	7,803,364	8,645,249	11,922,192
Class C Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(25,000)		0
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	0	0	0
Outstanding	10,983,145	13,568,665	14,226,435	13,184,527
Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(43,091)	(17,289)	(67,255)
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)		(17,289)	(67,255)
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(32,805)	0	(2,026,453)
Common Stock | Class C Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(32,805)	0	(2,026,453)
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)		(1,499,655)	(1,590,611)
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(1,535,275)	(841,885)	(606,066)
Common Stock | Class C Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(2,593,325)	(657,770)	(984,545)
Unvested restricted share-based awards
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(916,085)	(959,000)	(1,517,724)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	5,293,642	5,005,422	4,678,457	4,013,986
Unvested restricted share-based awards | Class A Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(916,085)	(959,000)	(1,517,724)
Unvested restricted share-based awards | Class B Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	0	0	0
Unvested restricted share-based awards | Class C Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	0	0	0
Performance Shares
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	60,000	0
Performance Shares | Pro Forma
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	90,000

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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