Quarterly report pursuant to Section 13 or 15(d)

Quarterly report pursuant to Section 13 or 15(d)

Goodwill and Intangible Assets - Narrative (Detail)

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Goodwill and Intangible Assets - Narrative (Detail) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]          
Goodwill $ 147,019,000   $ 147,019,000   $ 147,019,000
Changes in carrying amount of goodwill     0   $ 0
Amortization of intangibles $ 1,400,000 $ 1,700,000 $ 2,834,000 $ 3,450,000