Revenues - Revenues Disaggregated by Revenue Stream (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	$ 78,748	$ 67,654	$ 153,721	$ 135,442
Total revenues	264,414	247,329	525,445	494,244
Fiber Infrastructure
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	75,849	64,071	147,787	128,055
Total revenues	81,327	67,389	158,160	134,356
Fiber Infrastructure | Lit Backhaul
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	33,401	33,474	65,606	66,820
Fiber Infrastructure | Enterprise and Wholesale
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	19,241	15,562	35,970	30,980
Fiber Infrastructure | E-Rate and Government
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	22,533	14,157	44,528	28,387
Fiber Infrastructure | Other
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	674	878	1,683	1,868
Consumer CLEC
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	2,899	3,583	5,934	7,387
Total revenues	2,899	3,583	5,934	7,387
ASC 2014-09
Disaggregation Of Revenue [Line Items]
Total revenues	$ 185,666	$ 179,675	$ 371,724	$ 358,802