Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Fair value of all asset derivatives designated as cash flow hedging instruments.

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Net fair value of all derivative instruments designated as cash flow hedging instruments, which is ordinarily reflected within other comprehensive income.

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

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

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

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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.

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Percentage of principal amount of debt redeemed.

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Amount, after accumulated amortization, of debt discount.

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Notes Payable (Details)	1 Months Ended		12 Months Ended
Notes Payable (Details)	Oct. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) instrument	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) derivative	Sep. 30, 2018 USD ($) derivative	Sep. 30, 2017 USD ($) derivative	Oct. 31, 2015 USD ($) derivative	May 31, 2014 USD ($) derivative	Apr. 30, 2013 USD ($) derivative
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| instrument			0
Repayment of notes payable			$ 300,000,000	$ 250,000,000	$ 0
Payment of make-whole premium			18,240,000	0	$ 0
Long-term debt maturities for the next five years			675,000,000
Loans Payable
Debt Instrument [Line Items]
Debt issuance costs			26,932,000	$ 22,682,000
2022 Notes
Debt Instrument [Line Items]
Principal			325,000,000
Discount			4,989,000
Net Price			$ 320,011,000
Stated Rate			3.80%
Effective Rate			3.985%
2023 Notes
Debt Instrument [Line Items]
Principal			$ 350,000,000
Discount			2,594,000
Net Price			$ 347,406,000
Stated Rate			3.30%
Effective Rate			3.388%
2023 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative										4
Notional amount										$ 240,000,000
Liability amount from termination of hedge agreement										3,156,000
Liability amount from termination of hedge agreement, comprehensive income										$ 3,141,000
2024 Notes
Debt Instrument [Line Items]
Principal			$ 350,000,000
Discount			707,000
Net Price			$ 349,293,000
Stated Rate			3.90%
Effective Rate			3.924%
2024 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative									3
Notional amount									$ 225,000,000
Liability amount from termination of hedge agreement									$ 6,312,000
2025 Notes
Debt Instrument [Line Items]
Principal			$ 400,000,000
Discount			964,000
Net Price			$ 399,036,000
Stated Rate			4.00%
Effective Rate			4.029%
2025 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative								4
Notional amount								$ 300,000,000
Liability amount from termination of hedge agreement								$ 13,369,000
2026 Notes
Debt Instrument [Line Items]
Principal			$ 350,000,000
Discount			3,860,000
Net Price			$ 346,140,000
Stated Rate			3.60%
Effective Rate			3.733%
2026 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative					2
Notional amount					$ 180,000,000
Gain amount from termination of hedge agreement					$ 13,345,000
2027 Notes
Debt Instrument [Line Items]
Principal			$ 400,000,000
Discount			1,628,000
Net Price			$ 398,372,000
Stated Rate			3.50%
Effective Rate			3.548%
2027 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative							2
Notional amount							$ 250,000,000
Liability amount from termination of hedge agreement							7,690,000
Liability amount from termination of hedge agreement, comprehensive income							$ 7,688,000
2028 Notes
Debt Instrument [Line Items]
Principal			$ 400,000,000
Discount			2,848,000
Net Price			$ 397,152,000
Stated Rate			4.30%
Effective Rate			4.388%
2028 Notes \| Forward Starting Swaps
Debt Instrument [Line Items]
Number of derivative financial instruments outstanding \| derivative						2
Notional amount						$ 250,000,000
Gain amount from termination of hedge agreement						$ 4,080,000
2048 Notes
Debt Instrument [Line Items]
Principal			$ 300,000,000
Discount			4,239,000
Net Price			$ 295,761,000
Stated Rate			4.80%
Effective Rate			4.89%
2017 Notes
Debt Instrument [Line Items]
Stated Rate		6.875%
Repayment of notes payable		$ 250,000,000
2021 Notes
Debt Instrument [Line Items]
Stated Rate	5.50%
Repayment of notes payable	$ 300,000,000
Redemption price percentage	100.00%
Payment of make-whole premium	$ 18,240,000