Income Taxes - Provision (benefit) for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Income Tax Expense (Benefit):
Federal	$ 0	$ 0	$ (4)
State	26	96	132
Foreign	2,917	465	65
Current income tax provision (benefit)	2,943	561	193
Deferred Income Tax Expense (Benefit):
Deferred Federal Income Tax Expense (Benefit)	(2,357)	0	80,586
State	41	(53)	1,119
Foreign	(1,312)	(3,904)	(1,993)
Deferred income tax provision (benefit)	(3,628)	(3,957)	79,712
Tax provision (benefit):
Federal	(2,357)	0	80,582
State	67	43	1,251
Foreign	1,605	(3,439)	(1,928)
Income tax provision (benefit)	$ (685)	$ (3,396)	$ 79,905