Deferred Rent and Other Long Term Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Other Liabilities Noncurrent [Line Items]
Deferred rent liability	$ 13,399	$ 12,213
Retirement benefit obligations	6,829	6,629
Capital lease obligations	21	128
Derivative liability		3
Total	$ 20,249	$ 18,973