Annual report pursuant to Section 13 and 15(d)

Goodwill and Identified Intangible Assets - Change in Carrying Amount of Goodwill (Detail)

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Goodwill and Identified Intangible Assets - Change in Carrying Amount of Goodwill (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Goodwill [Roll Forward]    
Beginning balance $ 751,052 $ 259,938
Goodwill acquired 304,162 491,079
Measurement period and other adjustments (2,095) 35
Ending balance $ 1,053,119 $ 751,052