Income Taxes (Schedule of Components of Income (Loss) before Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ 334,900	$ 202,400	$ (26,500)
Foreign	36,900	23,400	(41,200)
Income (loss) before income taxes	$ 371,826	$ 225,819	$ (67,746)