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Activity Related to Unrecognized Tax Benefits (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Unrecognized tax benefit beginning Balance $ 34,112 $ 33,074 $ 23,854
Increases related to prior year tax positions 0 260 6,636
Increases related to current year tax positions 3,291 2,211 2,584
Expiration of the statute of limitations for the assessment of taxes 0 (1,433) 0
Unrecognized tax benefit ending Balance $ 37,403 $ 34,112 $ 33,074