Corporate Income Taxes - Components of Deferred Tax Assets, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Basis differences in depreciation and amortization	$ 0	$ 10,073
Deferred lease liabilities	15,638	23,527
Deferred revenue	4,590	8,247
Deferred compensation expense incurred in connection with stock options	912	994
Federal and state net operating loss carry-forwards	15,645	8,473
Accruals, reserves and other	4,942	7,297
Deferred tax assets, gross	41,727	58,611
Deferred tax liabilities
Deferred costs	1,740	803
Basis differences in depreciation and amortization	1,311	0
Change in accounting method	0	3,147
Undistributed foreign earnings and other	0	529
Deferred tax liabilities, gross	3,051	4,479
Gross deferred tax assets	38,676	54,132
Valuation allowance	(38,769)	(54,193)
Deferred tax liabilities, net	$ (93)	$ (61)