Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax credits	$ 11,727	$ 11,877
Tax loss carryforwards	129,808	130,314
Other	3,686	3,723
Deferred tax assets, gross	145,221	145,914
Valuation allowance	(144,593)	(145,259)
Deferred income tax assets, net	628	655
Property basis difference	(9,086)	(9,104)
Net deferred tax liabilities	$ (8,458)	$ (8,449)