Schedule of Industry and Rate Sensitivity (Detail) - USD ($) $ in Thousands	Mar. 31, 2017		Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	$ 841,265	[1]	$ 773,274	[2]
Aircraft and Parts
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	31,999		32,067
Commercial Fishing
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	38,816		40,600
Computer Programming, Data Processing and Other Computer Related Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	132,614		146,547
Drugs
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	33,837		34,042
Groceries and Related Products
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	14,865		14,856
Grocery Stores
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	23,689		23,761
Home Health Care Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	24,176		39,205
Insurance Agents, Brokers and Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	77,636		77,658
Management and Public Relations
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	16,518		16,493
Medical and Dental Laboratories
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	17,215		17,292
Miscellaneous Business Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	84,524		84,486
Miscellaneous Equipment Rental and Leasing
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	19,623
Miscellaneous Health and Allied Services, Not Elsewhere Classified
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	9,764		9,791
Miscellaneous Nonmetallic Minerals, Except Fuels
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	24,694		24,688
Miscellaneous Plastic Products
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	26,996		27,036
Motor Vehicles and Motor Vehicle Parts and Supplies
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	12,291		12,319
Offices and Clinics of Doctors of Medicine
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	92,171		83,386
Personnel Supply Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	34,726		36,921
Public Warehousing and Storage
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	55,287
Research, Development and Testing Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	17,744		17,744
Schools and Educational Services, Not Elsewhere Classified
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	20,916		20,979
Surgical, Medical, and Dental Instruments and Supplies
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	13,240		13,403
Telephone Communications
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	17,924
Fixed Rate
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	88,926		88,877
Fixed Rate | Insurance Agents, Brokers and Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	4,402		4,391
Fixed Rate | Miscellaneous Business Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	84,524		84,486
Floating Rate
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	752,339		684,397
Floating Rate | Aircraft and Parts
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	31,999		32,067
Floating Rate | Commercial Fishing
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	38,816		40,600
Floating Rate | Computer Programming, Data Processing and Other Computer Related Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	132,614		146,547
Floating Rate | Drugs
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	33,837		34,042
Floating Rate | Groceries and Related Products
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	14,865		14,856
Floating Rate | Grocery Stores
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	23,689		23,761
Floating Rate | Home Health Care Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	24,176		39,205
Floating Rate | Insurance Agents, Brokers and Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	73,234		73,267
Floating Rate | Management and Public Relations
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	16,518		16,493
Floating Rate | Medical and Dental Laboratories
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	17,215		17,292
Floating Rate | Miscellaneous Equipment Rental and Leasing
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	19,623
Floating Rate | Miscellaneous Health and Allied Services, Not Elsewhere Classified
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	9,764		9,791
Floating Rate | Miscellaneous Nonmetallic Minerals, Except Fuels
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	24,694		24,688
Floating Rate | Miscellaneous Plastic Products
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	26,996		27,036
Floating Rate | Motor Vehicles and Motor Vehicle Parts and Supplies
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	12,291		12,319
Floating Rate | Offices and Clinics of Doctors of Medicine
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	92,171		83,386
Floating Rate | Personnel Supply Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	34,726		36,921
Floating Rate | Public Warehousing and Storage
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	55,287
Floating Rate | Research, Development and Testing Services
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	17,744		17,744
Floating Rate | Schools and Educational Services, Not Elsewhere Classified
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	20,916		20,979
Floating Rate | Surgical, Medical, and Dental Instruments and Supplies
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	13,240		$ 13,403
Floating Rate | Telephone Communications
Schedule of Held-to-maturity Securities [Line Items]
Corporate debt	$ 17,924

[1] As a result of a change to a clearing organization's rulebook effective January 3, 2017, beginning with the first quarter 2017 the Company is presenting the fair value of centrally cleared interest rate swaps adjusted for $673.2 million of variation margin. The variation margin was previously reported under cash and cash equivalents and is currently reported as a reduction to interest rate swaps, at fair value. Prior period balances will not be adjusted.

[2] Derived from the audited consolidated financial statements at December 31, 2016.