Employee Benefit Plans (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	Dec. 31, 2013
Employee Benefit Plans [Line Items]
Target asset allocation, fixed income investments, percentage					100.00%	49.00%
Amount of unamortized losses in other comprehensive income			$ 56,700
Additional company contributions to settle pension obligation			9,200
Pension Benefits
Components of the net periodic benefit cost
Service cost	$ 63	$ 47	118	$ 90
Interest cost	(1,118)	1,225	91	2,387
Expected return on plan assets	1,561	(1,903)	0	(3,808)
Recognized net actuarial loss	388	260	758	467
Benefit cost (income)	894	(371)	967	(864)
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	210	156	450	343
Interest cost	386	362	792	755
Amortization of prior service cost	(136)	(136)	(272)	(272)
Recognized net actuarial loss	367	178	759	407
Benefit cost (income)	$ 827	$ 560	$ 1,729	$ 1,233