Subsequent Events (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Feb. 28, 2019 USD ($) derivative
Subsequent Event [Line Items]
Dividends declared		$ (503)	$ (2,961)
Subsequent Event
Subsequent Event [Line Items]
Number of interest rate swap agreements held | derivative				4
Derivative, Swap Type, Average Fixed Price				2.48%
Derivative, Notional Amount				$ 400,000
Dividends declared	$ (1,600)
Switch, Ltd. | Subsequent Event
Subsequent Event [Line Items]
Cash distributions to common unit holders (in dollars per share) | $ / shares	$ 0.0294
Cash distributions declared	$ 7,200
Class A | Subsequent Event
Subsequent Event [Line Items]
Dividends declared (in dollars per share) | $ / shares	$ 0.0294