Derivatives and Hedging Activities (Details) - USD ($) $ in Thousands				3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 19, 2018	Apr. 21, 2017	Apr. 09, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2019	Mar. 31, 2018	Dec. 31, 2017
Derivative instruments and hedging activities disclosures
Amount of gain (loss) recorded in accumulated other comprehensive income				$ 224	$ (323)	$ 833	$ (10)
Interest expense				$ 8,907	5,958	$ 16,645	11,065
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Amount of swap agreement	$ 75,000	$ 100,000	$ 75,000						$ 50,000	$ 50,000
Term of loan facility	5 years	5 years	5 years
Derivative, Fixed Interest Rate	4.12%			2.88%		2.88%				2.98%
Interest rate swap terminated		$ 50,000
Amount of gain (loss) recorded in accumulated other comprehensive income				$ (200)	300	$ 800
Amount reclassified to interest expense				(100)	200		500
Interest expense				8,900	$ 6,000	16,600	11,100
Derivative asset recognized in other assets				$ 1,900		1,900				$ 1,100
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging | Forecast
Derivative instruments and hedging activities disclosures
Amount estimated to be reclassified as an increase to interest expense								$ 700
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging | Maximum
Derivative instruments and hedging activities disclosures
Amount of gain (loss) recorded in accumulated other comprehensive income							$ (100)
Amount reclassified to interest expense						$ (100)
LIBOR | Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Reference rate	one-month LIBOR		one-month LIBOR
Derivative, Fixed Interest Rate				2.83%		2.83%				2.93%