Derivatives - Schedule of Derivative Instruments (Details) - Cash flow hedges $ in Thousands	Jun. 30, 2018 USD ($) instrument	Dec. 31, 2017 USD ($) instrument
Interest rate swaps
Derivative [Line Items]
Number of instruments | instrument	5	5
Amount expected to be reclassified to interest expense over the next 12 months	$ 1,690
Notional	450,000	$ 450,000
$100,000 interest rate swap maturing in 2018 no. 1
Derivative [Line Items]
Notional	$ 100,000
Fixed interest rate (as a percent)	1.26%
$100,000 interest rate swap maturing in 2018 no. 2
Derivative [Line Items]
Notional	$ 100,000
Fixed interest rate (as a percent)	1.26%
$100,000 interest rate swap maturing in 2021 no. 1
Derivative [Line Items]
Notional	$ 100,000
Fixed interest rate (as a percent)	2.00%
$100,000 interest rate swap maturing in 2021 no. 2
Derivative [Line Items]
Notional	$ 100,000
Fixed interest rate (as a percent)	2.00%
$50,000 interest rate swap maturing in 2021
Derivative [Line Items]
Notional	$ 50,000
Fixed interest rate (as a percent)	2.00%
LIBOR
Derivative [Line Items]
Reference rate for variable interest rate	one-month floating rate LIBOR