Income Taxes (Schedule of Components of Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	$ 162,639	$ 120,634	$ 146,915
Current State Tax Expense (Benefit)	14,301	11,252	15,713
Current Foreign Tax Expense (Benefit)	17,382	22,946	14,508
Current Income Tax Expense (Benefit)	194,322	154,832	177,136
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	(38,416)	12,140	12,563
Deferred State Income Tax Expense (Benefit)	(2,436)	2,515	1,300
Deferred Foreign Income Tax Expense (Benefit)	(7,813)	(3,013)	5,753
Deferred Income Tax Expense (Benefit)	(48,665)	11,642	19,616
Tax expense (benefit) relating to uncertain tax positions, including accrued interest	5,084	(1,612)	4,338
Income Tax Expense (Benefit)	$ 150,741	$ 164,862	$ 201,090