Stockholders' Equity (Details Textual) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Jan. 31, 2017 shares	Jan. 31, 2015	Dec. 31, 2016 USD ($) CustomerAccount shares	Dec. 31, 2014 CustomerAccount shares	Dec. 31, 2016 USD ($) CustomerAccount $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Stockholders Equity Transaction [Line Items]
Repurchase of common stock, shares					300,000
Remaining number of shares available for repurchase			6,700,000		6,700,000
Repurchase of common stock for employee tax withholdings, shares					344,000	265,000	252,000
Repurchase of common stock for tax withholdings, value | $					$ 13,700	$ 8,100	$ 6,900
Cash dividends declared per common share | $ / shares					$ 0.74	$ 0.70	$ 0.62
Cash dividend | $					$ 23,800	$ 22,900
Stock warrants term							10 years
Stock warrants, exercise price | $ / shares							$ 26.68
Additional number of Residential Customer Accounts converted | CustomerAccount					5,000,000
Stock warrants outstanding			2,851,000		2,851,000	2,851,000
Current portion of long-term debt conversion obligation | $			$ 39,841		$ 39,841
Senior Subordinated Convertible Notes 2010
Stockholders Equity Transaction [Line Items]
Carrying amount of the equity component of convertible notes | $						$ 22,900
Current portion of long-term debt conversion obligation | $			40,000		40,000
Senior Convertible Notes 2016
Stockholders Equity Transaction [Line Items]
Carrying amount of the equity component of convertible notes | $			$ 9,800		$ 9,800
Migration Of Comcast Current Residential Customer Accounts
Stockholders Equity Transaction [Line Items]
Issuance of stock warrants				1,900,000			1,900,000
Migration Of Comcast Current Residential Customer Accounts | First 25 % of Stock Warrants
Stockholders Equity Transaction [Line Items]
Vesting percentage of stock warrants				25.00%
Number of customer account converted | CustomerAccount				500,000
Number of stock warrants vesting				500,000
Conversion Of Comcast Current Residential Customer Accounts | Second 25 % of Stock Warrants
Stockholders Equity Transaction [Line Items]
Vesting percentage of stock warrants		25.00%
Vesting date of stock warrants					2015-01
Conversion Of Comcast Current Residential Customer Accounts | Third 25 % of Stock Warrants
Stockholders Equity Transaction [Line Items]
Vesting percentage of stock warrants			25.00%
Number of customer account converted | CustomerAccount			5,500,000
Conversion Of Comcast Current Residential Customer Accounts | Last 25 % of Stock Warrants
Stockholders Equity Transaction [Line Items]
Vesting percentage of stock warrants					25.00%
Number of customer account converted | CustomerAccount					5,700,000
Total target of customer account conversions | CustomerAccount					11,200,000
Conversion Of Comcast Acquired Additional Residential Customer Accounts
Stockholders Equity Transaction [Line Items]
Issuance of stock warrants			1,000,000		1,000,000
Comcast
Stockholders Equity Transaction [Line Items]
Issuance of stock warrants				2,900,000			2,900,000
Amount of unvested stock warrants that become vested upon a fundamental change of the Company					50.00%
Beneficial ownership required for potential cash settlement			19.99%		19.99%
Stock warrants exercised					0
Comcast | Subsequent Event
Stockholders Equity Transaction [Line Items]
Stock warrants exercised	1,400,000
Net share settlement of treasury shares upon exercise of stock warrants	649,000
Stock warrants outstanding	1,500,000
Remaining number of stock warrants vested	0
Comcast | Stock Warrants
Stockholders Equity Transaction [Line Items]
Client contract incentive related to stock warrants | $					$ 16,000	7,300
Accumulated amortization expense of client contract incentive related to stock warrants | $					$ 4,300	$ 2,000
SEC Rule 10b5-1 Plan
Stockholders Equity Transaction [Line Items]
Repurchase of common stock, shares					300,000	300,000	700,000
Total amount paid | $					$ 11,600	$ 6,900	$ 19,100
Weighted-average price per share | $ / shares					$ 36.42	$ 27.06	$ 26.05
ASR Agreement
Stockholders Equity Transaction [Line Items]
Repurchase of common stock, shares						1,600,000
Weighted-average price per share | $ / shares						$ 31.64
Accelerated share repurchase agreement, total amount paid | $						$ 50,000