Defined Benefit Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Service cost	$ 671	$ 706	$ 1,432	$ 1,404
Interest cost	8,045	8,996	16,272	17,914
Expected return on assets	(10,323)	(11,600)	(20,824)	(23,062)
Amortization of actuarial loss	2,952	2,840	6,264	5,844
Net periodic benefit cost	$ 1,345	$ 942	$ 3,144	$ 2,100