Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 1,669	$ 1,303	$ 3,338	$ 2,606
Interest cost	1,500	1,468	3,000	2,936
Expected return on plan assets	(1,950)	(1,739)	(3,900)	(3,478)
Amortization of net loss	1,136	544	2,272	1,088
Net periodic benefit cost	2,355	1,576	4,710	3,152
Estimated 2015 pension plan contribution, disclosed in prior year 10K					$ 6,352
Contribution by employer			3,161
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	1,305	924	2,610	1,848
Interest cost	713	586	1,426	1,172
Expected return on plan assets	0	0	0	0
Amortization of net loss	731	224	1,462	448
Net periodic benefit cost	$ 2,749	$ 1,734	$ 5,498	$ 3,468