Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Income Tax Assets And Liabilities [Line Items]
Asset reserves and liabilities not yet deductible for tax	$ 21,742	$ 19,045
Tax over book basis of certain assets	1,665	40
Net operating loss and tax credit carryforwards	5,483	5,040
Intangible contract value	148
Other	123	172
Total noncurrent deferred tax assets	29,161	24,297
Less valuation allowance	(3,986)	(3,308)
Total noncurrent deferred tax assets	25,175	20,989
Book over tax basis of certain assets	(5,707)	(5,959)
Intangible value	(2,370)
Other	(2,151)	(2,216)
Total noncurrent deferred tax liabilities	(10,228)	(8,175)
Net total noncurrent deferred tax assets	$ 14,947	$ 12,814