Employee Benefit Plans (Defined Benefit Plans Disclosure) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,570	$ 2,819	$ 6,224	$ 5,399
Interest cost	1,357	1,431	2,687	2,629
Expected return on plan assets	(2,213)	(1,823)	(3,767)	(3,108)
Amortization of prior service cost	82	95	165	169
Amortization of prior actuarial loss	769	1,082	1,863	2,163
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	256	0	513
Total	3,565	3,860	7,172	7,765
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	636	721	1,272	1,442
Interest cost	529	565	1,059	1,130
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(329)	(155)	(658)	(311)
Amortization of prior actuarial loss	498	457	996	914
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	0	0	0
Total	$ 1,334	$ 1,588	$ 2,669	$ 3,175