Financial Instruments and Risk Management - Narrative (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015 derivative_instrument	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Interest rate derivative losses reclassified into earnings, net of tax		$ 241,000	$ (37,000)	$ 224,000
Loss reclassified from AOCI into income, tax		75,000	372,000	130,000
Accumulated other comprehensive loss		1,193,000	1,464,000	$ 1,345,000
Interest rate swap
Derivative [Line Items]
Number of interest rate derivatives settled | derivative_instrument	6
Accumulated other comprehensive loss		1,100,000	1,400,000
Interest rate swap | Cash flow hedge
Derivative [Line Items]
Unrealized gain (loss) on interest rate derivative instruments		0	0
Loss reclassified from AOCI into earnings		316,000	335,000
Interest rate derivative losses reclassified into earnings, net of tax		$ 241,000	$ (37,000)