Concentrations of Credit Risk - Commercial Real Estate Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Commercial Mortgages
Office	$ 811.2	$ 825.2
Apartment/ Multi-family	490.7	623.3
Retail	529.7	631.1
Industrial/ Warehouse	254.9	311.1
Other	426.6	445.6
Total Commercial Mortgages	2,513.1	2,836.3
Construction, Acquisition and Development Loans	420.6	350.8
Single Family Investment	127.0	164.8
Other Commercial Real Estate Related	168.1	130.8
Total Commercial Real Estate Loans	$ 3,228.8	$ 3,482.7

Commercial Mortgages [Abstract]

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Loans Receivable Commercial Construction Acquisition And Development

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Loans Receivable, Commercial Real Estate, Commercial Mortgage, Apartments And Multi Family

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Loans Receivable, Commercial Real Estate, Commercial Mortgage, Industrial And Warehouse

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Loans Receivable, Commercial Real Estate, Commercial Mortgage, Office

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Loans Receivable, Commercial Real Estate, Commercial Mortgage, Other

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Loans Receivable, Commercial Real Estate, Commercial Mortgage, Retail

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Loans receivable - commercial real estate - single family investment

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Amount before allowance of mortgage loans on existing land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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-Publisher FASB
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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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-Subparagraph (SX 210.9-03.7(a))
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