Defined Pension Plans (Schedule of Net Periodic Pension Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	$ 3,527	$ 3,796
Interest cost on projected benefit obligation	3,480	3,178
Expected return on plan assets	(4,734)	(4,864)
Net amortization	1,200	1,542
Net periodic pension cost	3,473	3,652
Unfunded Supplemental Executive Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	133	140
Interest cost on projected benefit obligation	367	348
Net amortization	295	654
Net periodic pension cost	$ 795	$ 1,142