Description of the business and summary of significant accounting policies: (Tables)

12 Months Ended

Dec. 31, 2016

Description of the business and summary of significant accounting policies:

Schedule of depreciation and amortization periods

Type of asset	Depreciation or amortization period
Indefeasible rights of use (IRUs)	Shorter of useful life or the IRU lease agreement; generally 15 to 20 years
Network equipment	3 to 8 years
Leasehold improvements	Shorter of lease term, including reasonably assured renewal periods, or useful life
Software	5 years
Owned buildings	40 years
Office and other equipment	3 to 7 years
System infrastructure	5 to 10 years

Schedule of diluted weighted average shares

	Year Ended December 31, 2016		Year Ended December 31, 2015		Year Ended December 31, 2014
Weighted average common shares—basic		44,641,805		44,888,723		45,960,720
Dilutive effect of stock options		31,760		40,196		59,196
Dilutive effect of restricted stock		199,465		230,570		329,754
Weighted average common shares—diluted		44,873,030		45,159,489		46,349,670

Schedule of unvested and anti-dilutive shares

	December 31, 2016		December 31, 2015		December 31, 2014
Unvested shares of restricted common stock		908,761		870,751		1,282,646
Anti-dilutive options for common stock		90,959		119,872		84,690
Anti-dilutive shares of restricted common stock		79,450		362,241		379,639