Organization, Consolidation and Presentation of Financial Statements - Additional Information (Detail) $ / shares in Units, Record in Millions				3 Months Ended				6 Months Ended
	Mar. 02, 2017 USD ($) $ / shares	Jan. 01, 2017 USD ($)	Jun. 21, 2016 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) shares	Jun. 30, 2017 USD ($) Record	Jun. 30, 2016 USD ($)	May 09, 2017 $ / shares
Basis Of Presentation [Line Items]
ILEC, CLEC and VoIP records managed | Record								223
Income tax expense				$ 22,652,000		$ 18,389,000		$ 44,233,000	$ 43,235,000
Effective income tax rate				33.60%		35.80%		30.90%	35.80%
Uncertain tax positions					$ 15,700,000
Future Dividend payment suspension announcement date								May 09, 2017
Per common share quarterly dividend | $ / shares	$ 0.225
Total dividend paid to shareholders	$ 18,800,000
Dividends Payable, Date of Record								Feb. 21, 2017
Share repurchase program, authorized amount							$ 75,000,000
Number of common stock shares purchased | shares							1,000,000
Aggregate share purchase price							$ 22,000,000	$ 0	$ 21,961,000
Proceeds from the sale of property and equipment			$ 38,800,000					$ 409,000	$ 38,368,000
Gain loss on disposition of assets and leaseback transaction			19,000,000
leaseback agreement period								12-year
Deferred gain on sales-leaseback agreement			$ 6,100,000
Increased our retained deficit		$ 100,000
Excess tax benefits on stock options recognized in additional paid-in capital								$ 300,000
Apollo Global Management, LLC [Member]
Basis Of Presentation [Line Items]
Acquired price per share | $ / shares										$ 23.50