Pensions (Details) - Pension Plans [Member] - 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
Net Periodic Pension Cost [Abstract]
Service cost	$ 292	$ 238	$ 583	$ 476
Interest cost	379	361	758	722
Expected return on plan assets	(558)	(497)	(1,115)	(994)
Amortization of actuarial loss	176	32	352	63
Amortization of prior service cost	(3)	(3)	(6)	(6)
Rate-regulated adjustment	289	444	578	771
Net periodic pension expense	$ 575	$ 575	1,150	$ 1,032
Employer Contributions [Abstract]
Estimated employer contributions in 2015					$ 2,300
Contributions made by employer			$ 2,300