Defined Benefit Plans - Net Periodic Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Contributions by Employer	$ 1,900		$ 2,600
Service costs	230	$ 190	470	$ 380
Interest costs	410	440	830	880
Expected return on plan assets	(490)	(520)	(1,010)	(1,040)
Amortization of prior service cost	10	10	10	10
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	(2,750)	0	(2,750)	0
Amortization of net (gain)/loss	360	280	740	560
Net periodic benefit cost	3,270	400	3,790	790
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	0	0	0	0
Interest costs	0	10	10	20
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0	0	0	0
Amortization of net (gain)/loss	(10)	(30)	(20)	(50)
Net periodic benefit cost	$ (10)	$ (20)	$ (10)	$ (30)