Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Components of Net Periodic Benefit Cost
Service cost	$ 250	$ 249	$ 501	$ 497	$ 995
Interest cost	307	289	617	578	$ 1,155
Net loss	73	53	145	107
Net periodic pension cost	$ 630	$ 591	$ 1,263	$ 1,182