Benefit Plans (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2016

Dec. 31, 2015

Benefit Plans

Schedule of components of net periodic benefit cost

	Pension Benefits				Other Benefits
(dollars in thousands)	2016		2015		2016		2015
Three Months Ended September 30,
Service cost	$	215	$	202	$	193	$	176
Interest cost		2,172		2,166		210		198
Expected return on plan assets		(1,180)		(1,042)		—		—
Prior service credit		—		—		(107)		(107)
Recognized net actuarial loss		1,774		2,451		—		34
Total net periodic benefit cost	$	2,981	$	3,777	$	296	$	301
Nine Months Ended September 30,
Service cost	$	644	$	605	$	577	$	527
Interest cost		6,486		6,498		631		594
Expected return on plan assets		(3,515)		(3,125)		—		—
Prior service credit		—		—		(321)		(322)
Recognized net actuarial loss		5,319		7,353		—		103
Total net periodic benefit cost	$	8,934	$	11,331	$	887	$	902

	Pension Benefits				Other Benefits
(dollars in thousands)	2015		2014		2015		2014
Service cost	$	809	$	702	$	734	$	742
Interest cost		8,681		8,995		770		925
Expected return on plan assets		(4,178)		(4,270)		—		—
Prior service credit		—		—		(429)		—
Recognized net actuarial loss		9,928		5,163		32		—
Total net periodic benefit cost	$	15,240	$	10,590	$	1,107	$	1,667