Long-Term Debt - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	May 05, 2020		Dec. 31, 2019
Debt Instrument [Line Items]
Document Period End Date		Mar. 31, 2020
Long-term debt including current maturities		$ (456,600)			$ (486,600)
Debt Instrument, Unused Borrowing Capacity, Amount		10,000	$ 310,000
NYL Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities	[1]	$ (40,000)
Debt Instrument, Interest Rate, Stated Percentage		2.96%
Uncollateralized Senior Note Due August Two Thousand Thirty Nine [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ (100,000)			(100,000)
Debt Instrument, Interest Rate, Stated Percentage		3.98%
Uncollateralized Senior Note Due December Two Thousand Thirty Four [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.98%
Term Note Due January Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ (70,000)			(70,000)
Debt Instrument, Interest Rate, Stated Percentage		2.80%
Term Note Due February Two Thousand Twenty [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ 0			(30,000)
Debt Instrument, Interest Rate, Stated Percentage		2.84%
3.48% note, due May 31, 2038 [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ (50,000)			(50,000)
3.25% note, due April 30, 2032 [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities		$ (70,000)			$ (70,000)
Prudential Unfunded Commitments [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.98%
Prudential Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt including current maturities	[2]	$ (50,000)
Debt Instrument, Interest Rate, Stated Percentage		3.00%
MetLife [Member] | Notes Payable, Other Payables [Member] | Shelf Notes [Member]
Debt Instrument [Line Items]
Maturity date term		20 years
New York Life [Member] | Notes Payable, Other Payables [Member] | Shelf Notes [Member]
Debt Instrument [Line Items]
Maturity date term		20 years
Prudential [Member] | Notes Payable, Other Payables [Member] | Shelf Notes [Member]
Debt Instrument [Line Items]
Senior notes		$ 150,000
Maturity date term		20 years
Debt Instrument, Interest Rate, Stated Percentage		3.25%
Prudential [Member] | Shelf Notes [Member]
Debt Instrument [Line Items]
Senior notes		$ 150,000
MetLife [Member]
Debt Instrument [Line Items]
Senior notes	[3]		150,000
Debt Instrument, Unused Borrowing Capacity, Amount		150,000	$ 150,000	[3]
New York Life [Member]
Debt Instrument [Line Items]
Senior notes		100,000
Debt Instrument, Unused Borrowing Capacity, Amount		50,000
Debt Instrument, Unused Borrowing Capacity, Amount	[1]	$ 10,000

[1] ⁽²⁾ In February 2020, we requested and NYL accepted our request to purchase $40.0 million of our unsecured debt.

[2] ⁽¹⁾ In January 2020, we requested and Prudential accepted our request to purchase $50.0 million of our unsecured debt.

[3] ⁽⁴⁾ In April 2020, we agreed to commercial terms with MetLife to provide a new $150.0 million MetLife Shelf Agreement for a three-year term ending March 31, 2023. The MetLife Shelf Agreement will be finalized in May 2020.