Goodwill and Intangible Assets - Change in Goodwill (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Goodwill [Line Items]
Beginning of the year	$ 208
End of the year	20,221
James & Sons Insurance [Member]
Goodwill [Line Items]
Effect of adjustments	636
OLCB [Member]
Goodwill [Line Items]
Acquired goodwill	19,168
Eich Brothers Insurance [Member]
Goodwill [Line Items]
Acquired goodwill	$ 209

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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