Income Taxes (Schedule of Income Taxes Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax at federal statutory rate	$ 74,495	$ 69,710	$ 40,029
State income tax, net of federal income tax impact	6,011	6,480	4,386
Foreign tax rate differential	(322)	(614)	(82)
Domestic production deduction	(5,511)	(5,067)	(2,336)
Share-based payment compensation	(7,683)	0	0
Federal tax credits	(1,110)	(1,736)	(919)
Changes in tax law (TCJA)	13,210	0	0
Other	870	728	(1,054)
Provision for income taxes	$ 79,960	$ 69,501	$ 40,024

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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