Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 1,623	$ 1,669
Interest cost	1,663	1,500
Expected return on plan assets	(1,988)	(1,950)
Amortization of net loss	992	1,136
Net periodic benefit cost	2,290	2,355
Estimated 2015 pension plan contribution, disclosed in prior year 10K			$ 6,384
Contribution by employer	1,595
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	932	1,305
Interest cost	754	713
Expected return on plan assets	0	0
Amortization of net loss	379	731
Net periodic benefit cost	$ 2,065	$ 2,749