Segment Reporting - Composition of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Revenue	$ 99,328	$ 97,689	$ 92,101	$ 89,157	$ 81,888	$ 81,666	$ 80,832	$ 73,966	$ 378,275	$ 318,352	$ 265,870
Colocation
Revenue from External Customer [Line Items]
Revenue									304,720	259,046	218,498
Connectivity
Revenue from External Customer [Line Items]
Revenue									67,690	53,715	43,147
Other
Revenue from External Customer [Line Items]
Revenue									$ 5,865	$ 5,591	$ 4,225