Stockholders' Equity and Equity Compensation Plans (Details Textual) $ / shares in Units, $ in Thousands, CustomerAccount in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2016 CustomerAccount shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2014 $ / shares shares
Stockholders Equity And Equity Compensation Plans [Line Items]
Remaining number of shares available for repurchase		6,800,000		6,800,000
Repurchase of common stock for employee tax withholdings, shares				300,000	300,000
Repurchase of common stock for tax withholdings, value | $				$ 13,000	$ 8,000
Cash dividends declared per common share | $ / shares		$ 0.185	$ 0.175	$ 0.56	$ 0.53
Cash dividend | $		$ 6,000	$ 5,700	$ 18,000	$ 17,200
Stock warrants term						10 years
Stock warrants, exercise price | $ / shares						$ 26.68
Stock-based compensation expense | $		$ 5,200	$ 5,300	$ 17,273	$ 15,775
Performance Shares
Stockholders Equity And Equity Compensation Plans [Line Items]
Performance based awards granted to executive management shares				100,000
Vesting period				3 years
Restricted common stock
Stockholders Equity And Equity Compensation Plans [Line Items]
Vesting period		4 years		4 years
Migration Of Comcast Current Residential Customer Accounts
Stockholders Equity And Equity Compensation Plans [Line Items]
Number of stock warrants vesting				1,000,000
Migration Of Comcast Current Residential Customer Accounts | Subsequent Event
Stockholders Equity And Equity Compensation Plans [Line Items]
Number of stock warrants vesting	500,000
Number of customer account migrated | CustomerAccount	5.8
Comcast Corporation
Stockholders Equity And Equity Compensation Plans [Line Items]
Issuance of stock warrants						2,900,000
Client contract incentive related to stock warrants | $				$ 7,300
Amortization expense of client contract incentive related to stock warrants | $				$ 3,100
Stock warrants exercised				0
SEC Rule 10b5-1 Plan
Stockholders Equity And Equity Compensation Plans [Line Items]
Repurchase of common stock, shares				300,000	300,000
Total amount paid | $				$ 9,500	$ 7,000
Weighted-average price per share | $ / shares				$ 36.07	$ 27.06