Benefit Plans - Funded Status of Plan (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Change in Projected Benefit Obligation
Projected benefit obligation, beginning of period			$ 28,624	$ 25,935	$ 25,935
Service cost	$ 250	$ 249	751	746	995
Interest cost	307	$ 289	921	866	1,155
Actuarial loss			0		1,031
Benefits paid			(426)		(492)
Projected benefit obligation, end of period	29,870		29,870		28,624
Change in Plan Assets
Plan assets at fair value, beginning of period			0	$ 0	0
Company contributions			426		492
Benefits paid			(426)		(492)
Plan assets at fair value, end of period	0		0		0
Unfunded Status of the Plan	$ (29,870)		$ (29,870)		$ (28,624)