Income Taxes - Benefit (Provision) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Benefit (Provision):
Federal	$ 57,547	$ 45,518	$ 46,598
State	(2,479)	7,268	10,642
Foreign	2,448	1,124
Income Tax Rate Change	(99,528)
Expiration of Net Operating Losses and Research & Development Tax Credits			(155)
Income tax benefit (provision) before valuation allowance	(42,012)	53,910	57,085
Deferred tax valuation allowance	66,294	$ (53,910)	$ (57,085)
Income Tax Benefit (Provision)	$ 24,282