Goodwill and Intangible Assets - Summary of Gross Carrying Value and Weighted Average Amortization Period of Intangible Assets by Type (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 7,928
Indefinite-Lived Assets, Gross Carrying Amount	4,599
ASCO Customer Relationships
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 4,739
Finite-Lived Assets, Weighted Average Amortization Period	15 years
ASCO VOBA
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 1,694
Finite-Lived Assets, Weighted Average Amortization Period	4 years
BDM Broker Networks
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 1,002
Finite-Lived Assets, Weighted Average Amortization Period	15 years
BDM Trade Name
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 493
Finite-Lived Assets, Weighted Average Amortization Period	1 year
ASCO European Licenses
Intangible Assets [Line Items]
Indefinite-Lived Assets, Gross Carrying Amount	$ 2,463
NUAL Lloyd's Syndicate Capacity
Intangible Assets [Line Items]
Indefinite-Lived Assets, Gross Carrying Amount	$ 2,136