Stockholders' Equity and Equity Compensation Plans (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2020	May 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2014	Apr. 30, 2020
Stockholders Equity And Equity Compensation Plans [Line Items]
Remaining number of shares available for repurchase			4,700,000		4,700,000
Repurchase of common stock for employee tax withholdings, shares			4,000	4,000	163,000	112,000
Repurchase of common stock for tax withholdings, value			$ 100	$ 200	$ 7,800	$ 4,700
Cash dividends declared per common share			$ 0.235	$ 0.2225
Cash dividend			$ 7,800	$ 7,300	23,200	22,000
Stock warrants term							10 years
Stock warrants, exercise price							$ 26.68
Stock-based compensation expense					$ 14,088	13,295
Performance Shares
Stockholders Equity And Equity Compensation Plans [Line Items]
Performance based awards granted to executive management and certain key employees shares					100,000
Vesting maturity date					first quarter of 2022
Vesting period					2 years
Market-based Awards
Stockholders Equity And Equity Compensation Plans [Line Items]
Performance based awards granted to executive management and certain key employees shares					100,000
Vesting period					4 years
Restricted common stock | Minimum
Stockholders Equity And Equity Compensation Plans [Line Items]
Vesting period					2 years
Restricted common stock | Maximum
Stockholders Equity And Equity Compensation Plans [Line Items]
Vesting period					4 years
Separation Agreement
Stockholders Equity And Equity Compensation Plans [Line Items]
Stock-based compensation expense			4,000	$ 4,800	$ 14,100	$ 13,300
Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number	198,000
Reversal of stock-based compensation expense			2,700
Fair value of modified award recognized			$ 2,300		$ 8,300
Comcast
Stockholders Equity And Equity Compensation Plans [Line Items]
Issuance of stock warrants							2,900,000
Stock warrants issued			1,000,000.0		1,000,000.0
Stock warrants vested					0
Stock Incentive Plan 2005
Stockholders Equity And Equity Compensation Plans [Line Items]
Increase in number of shares approved for issuance under incentive plan		3,600,000
Number of shares approved for issuance under incentive plan		25,000,000.0						21,400,000
SEC Rule 10b5-1 Plan
Stockholders Equity And Equity Compensation Plans [Line Items]
Repurchase of common stock, shares			139,000	92,000	290,000	485,000
Total amount paid			$ 5,500	$ 4,700	$ 12,300	$ 20,600
Weighted-average price per share			$ 39.93	$ 51.09	$ 42.55	$ 42.37