Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 1,669	$ 1,303	$ 5,007	$ 3,909
Interest cost	1,500	1,468	4,500	4,404
Expected return on plan assets	(1,950)	(1,739)	(5,850)	(5,217)
Amortization of net loss	1,136	544	3,408	1,632
Net periodic benefit cost	2,355	1,576	7,065	4,728
Estimated 2015 pension plan contribution, disclosed in prior year 10K					$ 6,352
Contribution by employer			6,352
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	1,305	924	3,915	2,772
Interest cost	713	586	2,139	1,758
Expected return on plan assets	0	0	0	0
Amortization of net loss	731	224	2,193	672
Net periodic benefit cost	$ 2,749	$ 1,734	$ 8,247	$ 5,202