Bonds Payable (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2020 USD ($) bond	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) bond
Debt Instrument [Line Items]
Number of series of bonds \| bond	2		2
Interest payments	$ 5,000,000.0	$ 5,600,000
Carrying value, net of discounts	695,519,000		$ 695,324,000
Bonds Payable \| 2026 and 2025 Bonds Payable
Debt Instrument [Line Items]
Interest payments	6,400,000	$ 6,400,000
Bonds Payable \| 2026 and 2025 Bonds Payable \| Level 2
Debt Instrument [Line Items]
Estimated fair value of debt instrument	735,700,000		734,400,000
Carrying value, net of discounts	698,900,000		698,900,000
Bonds Payable \| 2026 Bonds Payable
Debt Instrument [Line Items]
Face amount of issued debt instrument	$ 350,000,000.0		$ 350,000,000.0
Maturity of debt instrument	10 years		10 years
Interest rate for debt instrument (percent)	3.65%		3.65%
Discount rate of face value of issued debt instrument (percent)	99.626%		99.626%
Bonds Payable \| 2025 Bonds Payable
Debt Instrument [Line Items]
Face amount of issued debt instrument	$ 350,000,000.0		$ 350,000,000.0
Maturity of debt instrument	10 years		10 years
Interest rate for debt instrument (percent)	4.15%		4.15%
Discount rate of face value of issued debt instrument (percent)	99.859%		99.859%

Debt Instrument, Discount Rate at Issuance of Face Value

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- Definition

Number Of Series Of Bonds

+ References

No definition available.

+ Details

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

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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

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4297-108586

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
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-Paragraph 1
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