Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Income Tax Assets And Liabilities [Line Items]
Asset reserves and liabilities not yet deductible for tax	$ 19,045	$ 29,198
Tax over book basis of certain assets	40	866
Net operating loss and tax credit carryforwards	5,040	5,487
Intangible contract value		2,570
Other	172	346
Total noncurrent deferred tax assets	24,297	38,467
Less valuation allowance	(3,308)	(3,436)
Total noncurrent deferred tax assets	20,989	35,031
Book over tax basis of certain assets	(5,959)	(9,386)
Intangible lease value		(8,368)
Other	(2,216)	(3,542)
Total noncurrent deferred tax liabilities	(8,175)	(21,296)
Net total noncurrent deferred tax assets	$ 12,814	$ 13,735