Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Loss
Balance, beginning of period	$ 499,194	$ 394,318
Balance, end of period	459,239	499,194
Accumulated Other Comprehensive Loss
Changes in Accumulated Other Comprehensive Loss
Balance, beginning of period	(5,260)	(5,468)
Other comprehensive income before reclassifications of gain (loss)	3	154
Amount of (loss) gain reclassified from accumulated other comprehensive income	181	54
Total other comprehensive (loss) income	184	208
Balance, end of period	(5,076)	(5,260)
Pension Plan
Changes in Accumulated Other Comprehensive Loss
Balance, beginning of period	(5,258)	(5,333)
Other comprehensive income before reclassifications of gain (loss)	3	21
Amount of (loss) gain reclassified from accumulated other comprehensive income	179	54
Total other comprehensive (loss) income	182	75
Balance, end of period	(5,076)	(5,258)
Derivatives
Changes in Accumulated Other Comprehensive Loss
Amount of (loss) gain reclassified from accumulated other comprehensive income	2
Total other comprehensive (loss) income	2
Derivatives pre-adoption
Changes in Accumulated Other Comprehensive Loss
Balance, beginning of period	$ (2)	(135)
Other comprehensive income before reclassifications of gain (loss)		133
Total other comprehensive (loss) income		133
Balance, end of period		$ (2)