New Financial Accounting Pronouncements - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash Reported within Condensed Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents	$ 35,556	$ 29,902
Total cash, cash equivalents and restricted cash	35,840	$ 30,659	$ 28,924	$ 48,006
ASU 2016-18 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents	35,556		27,166
Restricted cash	284		1,150
Restricted cash included within deferred charges and other assets			608
Total cash, cash equivalents and restricted cash	$ 35,840		$ 28,924