Debt - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Senior Notes due 2022
Debt Instrument [Line Items]
Senior notes principal amount	$ 600,000,000
Senior notes effective interest rate	3.97%
Senior notes proceeds	$ 593,900,000
Senior notes interest rate	3.95%
Frequency of senior notes payment	semi-annually in arrears on March 15 and September 15
Debt issuance cost	$ 1,377,000	$ 1,886,000
Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum loan borrowing capacity	200,000,000
Increase in commitment available	$ 300,000,000
Line of credit facility, interest rate description	Borrowings under the Credit Agreement generally bear interest for Base Rate Loans at a Base Rate equal to the highest of (i) a Federal Funds Rate plus one-half of one percent, (ii) Bank of America’s publicly announced “prime rate,” and (iii) the Eurodollar Rate plus one percent, plus the Applicable Rate which is based on the Company’s debt rating, or for Eurodollar Rate Loans, at the Eurodollar Rate equal to LIBOR plus the Applicable Rate.
Debt outstanding	$ 0
Credit Agreement \| Revolving Credit Facility \| Federal Funds Rate
Debt Instrument [Line Items]
Debt instrument, marginal interest rate	0.50%
Credit Agreement \| Revolving Credit Facility \| Eurodollar Rate
Debt Instrument [Line Items]
Debt instrument, marginal interest rate	1.00%
Credit Agreement \| Revolving Credit Facility \| Sublimit for Issuance of Letters of Credit
Debt Instrument [Line Items]
Maximum loan borrowing capacity	$ 100,000,000
Letters of credit outstanding	9,700,000
Credit Agreement \| Revolving Credit Facility \| Sublimit for Swing Line Commitment
Debt Instrument [Line Items]
Maximum loan borrowing capacity	$ 25,000,000
Repurchase Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Senior notes interest rate	3.663%
Maximum loan borrowing capacity	$ 150,000,000
Debt outstanding	0	$ 0
Borrowing base limitations	$ 0
Repurchase Agreement \| Revolving Credit Facility \| Minimum
Debt Instrument [Line Items]
Senior notes interest rate	1.85%

The Maximum Incremental Commitment amount is the sum of all incremental commitments under the repurchase facility.

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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- Definition

Fair value of the amount outstanding under the credit facility.

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- Definition

Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

+ References

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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- Definition

Carrying value as of the balance sheet date of the outstanding short-term borrowings under a revolving line of credit used by mortgage bankers to finance the origination or purchase of loans.

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