Stockholders Equity - (Details)		3 Months Ended			9 Months Ended		12 Months Ended
	May 19, 2015 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) class $ / shares shares	Mar. 31, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) class $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	Jun. 26, 2018 USD ($)	Dec. 14, 2017 USD ($)
Equity, Class of Stock [Line Items]
Common stock, shares authorized | shares		125,000,000			125,000,000
Preferred stock, shares authorized | shares		10,000,000			10,000,000		10,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.01			$ 0.01		$ 0.01
Number of classes | class		2			2
Preferred stock dividends declared		$ 1,698,000		$ 1,698,000	$ 5,094,000	$ 5,094,000
Convertible Preferred Stock, Shares Issued upon Conversion | shares	38.0619
Convertible Preferred Stock, Threshold Percentage of Stock Price Trigger					150.00%
Dividends, Cash		3,573,000		1,632,000	$ 9,388,000	4,144,000
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period			$ 346,900,000		346,900,000
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions					26,078,000	6,296,000
Purchase of treasury stock, cost					122,900,000
Treasury stock, cost, end of period		495,900,000			495,900,000		$ 346,900,000
Dividend Paid
Equity, Class of Stock [Line Items]
Dividends, Cash		3,000,000			8,200,000
Retained Earnings/(Accumulated deficit)
Equity, Class of Stock [Line Items]
Dividends, Cash		$ 3,573,000		1,632,000	$ 9,388,000	4,144,000
Treasury Stock
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period | shares			22,619,863		22,619,863
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions | shares					648,047
Treasury stock shares received, other | shares					1,155
Purchase of treasury stock, shares | shares					3,336,815
Treasury stock, shares, end of period | shares		26,605,880			26,605,880		22,619,863
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period			$ 346,870,000		$ 346,870,000
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions					26,078,000
Treasury stock received, value, other					29,000
Purchase of treasury stock, cost					122,945,000
Treasury stock, cost, end of period		$ 495,922,000			$ 495,922,000		$ 346,870,000
Treasury Stock, Average Cost Per Share [Roll Forward]
Treasury stock, average cost per share, beginning of period, in dollars per share | $ / shares			$ 15.33		$ 15.33
Shares purchased for minimum tax withholding under the Equity Plan or other similar transactions, Average Cost Per Share | $ / shares					40.24
Treasury stock received, average cost per share, other | $ / shares					25.33
Purchase of treasury stock, average cost per share, in dollars per share | $ / shares					36.84
Treasury stock, average cost per share, end of period, in dollars per share | $ / shares		$ 18.64			$ 18.64		$ 15.33
Additional Paid-in Capital | Convertible Debt
Equity, Class of Stock [Line Items]
Embedded Derivative, No Longer Bifurcated, Amount Reclassified to Stockholders' Equity			$ 29,600,000
Convertible Preferred Stock
Equity, Class of Stock [Line Items]
Stock Issued During Period, Shares, Other | shares	120,750
Preferred Stock, Dividend Rate, Percentage	5.625%
Proceeds from Issuance of Preferred Stock, net of issuance costs	$ 117,200,000
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	$ 3,600,000
Preferred Stock, Liquidation Preference Per Share | $ / shares	$ 1,000
Convertible Preferred Stock, Shares Issued upon Conversion | shares							38.488
Convertible Preferred Stock | Retained Earnings/(Accumulated deficit)
Equity, Class of Stock [Line Items]
Preferred stock dividends declared		$ 1,698,000		$ 1,698,000	$ 5,094,000	$ 5,094,000
Common Stock Class A
Equity, Class of Stock [Line Items]
Common stock, shares authorized | shares		62,500,000			62,500,000		62,500,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01			$ 0.01		$ 0.01
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period | shares			22,619,863		22,619,863
Treasury stock, shares, end of period | shares		26,605,880			26,605,880		22,619,863
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period			$ 346,870,000		$ 346,870,000
Treasury stock, cost, end of period		$ 495,922,000			$ 495,922,000		$ 346,870,000
Common Stock Class B
Equity, Class of Stock [Line Items]
Common stock, shares authorized | shares		62,500,000			62,500,000		62,500,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.01			$ 0.01		$ 0.01
Maximum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold					30 days
Minimum
Equity, Class of Stock [Line Items]
Convertible Preferred Stock, Threshold					20 days
Minimum | Call Option
Equity, Class of Stock [Line Items]
Option Indexed to Issuer's Equity, Strike Price | $ / shares					$ 26.27
Convertible Debt
Equity, Class of Stock [Line Items]
Unamortized discount							$ 6,700,000
Convertible Debt | 2022 convertible note
Equity, Class of Stock [Line Items]
Unamortized discount		$ 5,100,000			$ 5,100,000				$ 23,400,000
Option Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value								$ 29,000,000
Embedded Derivative, No Longer Bifurcated, Amount Reclassified to Stockholders' Equity							$ 29,600,000