Derivative Instruments and Hedging Activities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2014 USD ($) interest_rate_swap
Derivatives, Fair Value [Line Items]
Number of interest rate swaps | interest_rate_swap			2
Long-term debt, percentage bearing fixed interest, amount	$ 200,000
Long-term debt, percentage bearing variable interest, amount	36,000
5 year interest rate swap
Derivatives, Fair Value [Line Items]
Notional amount	$ 25,000
Fixed interest rate	2.50%
Maturity date	Aug. 29, 2024
Interest rate derivative assets	$ 180
Interest rate derivative liabilities		$ 492
10 year interest rate swap
Derivatives, Fair Value [Line Items]
Notional amount	$ 25,000
Fixed interest rate	1.73%
Maturity date	Aug. 29, 2019
Interest rate derivative assets	$ 108
Interest rate derivative liabilities		(70)
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional amount			$ 50,000
Interest rate derivative assets	288	(422)
Level 2 | 5 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative liabilities		492
Level 2 | 10 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative liabilities		(70)
Other Assets | Level 2 | 5 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative assets	180	70
Other Assets | Level 2 | 10 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative assets	$ 108
Interest rate derivative liabilities		$ (492)
LIBOR | Minimum
Derivatives, Fair Value [Line Items]
Derivative, basis spread on variable rate	1.25%
LIBOR | Maximum
Derivatives, Fair Value [Line Items]
Derivative, basis spread on variable rate	2.00%