Employee Benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Pension Plan
Net periodic benefit cost
Service cost		$ 1,623	$ 1,669	$ 4,869	$ 5,007
Interest cost		1,663	1,500	4,989	4,500
Expected return on plan assets		(1,988)	(1,950)	(5,964)	(5,850)
Amortization of net loss		992	1,136	2,976	3,408
Net periodic benefit cost		2,290	2,355	6,870	7,065
Estimated 2016 pension plan contribution, disclosed in prior year 10K						$ 6,384
Contribution by employer	$ 10			16,383
Postretirement Benefit Plan
Net periodic benefit cost
Service cost		932	1,305	2,796	3,915
Interest cost		754	713	2,262	2,139
Expected return on plan assets		0	0	0	0
Amortization of net loss		379	731	1,137	2,193
Net periodic benefit cost		$ 2,065	$ 2,749	$ 6,195	$ 8,247