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Stockholders' Equity Share Activity by Class (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	(82,729)	(77,442)	(48,646)
Outstanding	77,801,854	76,942,872	75,569,845	74,354,869
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	297,891	246,581	178,401
Class A Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues		(644,424)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	(82,729)	(77,442)	(48,646)
Outstanding	56,429,825	54,071,188	50,463,126	42,149,436
Class B Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues		(644,424)	(2,104,517)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	0	0	0
Outstanding	7,803,364	8,645,249	11,922,192	15,142,049
Class C Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues		0	(3,522,000)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	0	0	0
Outstanding	13,568,665	14,226,435	13,184,527	17,063,384
Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(17,289)	(67,255)	(3,628)
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)		(67,255)	(3,628)
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	0	(2,026,453)	(66,423)
Common Stock | Class C Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	0	(2,026,453)	(66,423)
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)		(1,590,611)	(1,472,197)
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(841,885)	(606,066)	(1,048,917)
Common Stock | Class C Common Stock
Class of Stock [Line Items]
Shares repurchased and retired during the period (shares)	(657,770)	(984,545)	(423,280)
Unvested restricted share-based awards
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(959,000)	(1,517,724)	(1,267,250)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	5,005,422	4,678,457	4,013,986	3,394,910
Unvested restricted share-based awards | Class A Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	(959,000)	(1,517,724)	(1,267,250)
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

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

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