Goodwill and Intangible Assets - Summary of Gross Carrying Value and Weighted Average Amortization Period of Intangible Assets by Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Jun. 30, 2018
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 6,604
Finite-Lived Assets, Accumulated Amortization	(333)
Indefinite-Lived Assets, Gross Carrying Amount	4,625
ASCO Customer Relationships
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	3,383
Finite-Lived Assets, Accumulated Amortization	$ (85)
Finite-Lived Assets, Weighted Average Amortization Period	10 years	15 years
ASCO VOBA
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 1,711
Finite-Lived Assets, Accumulated Amortization	$ (107)
Finite-Lived Assets, Weighted Average Amortization Period	4 years
BDM Broker Networks
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 1,012
Finite-Lived Assets, Accumulated Amortization	$ (17)
Finite-Lived Assets, Weighted Average Amortization Period	15 years
BDM Trade Name
Intangible Assets [Line Items]
Finite-Lived Assets, Gross Carrying Amount	$ 498
Finite-Lived Assets, Accumulated Amortization	$ (124)
Finite-Lived Assets, Weighted Average Amortization Period	1 year
ASCO European Licenses
Intangible Assets [Line Items]
Indefinite-Lived Assets, Gross Carrying Amount	$ 2,489
NUAL Lloyd's Syndicate Capacity
Intangible Assets [Line Items]
Indefinite-Lived Assets, Gross Carrying Amount	$ 2,136