Fair Value Measurments Debt Instruments (Carrying and fair value of debt) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Level 2
Carrying value and fair value of debt
Estimated fair value	$ 3,759,000	$ 3,984,699
Long Term Debt	3,759,000	3,759,000
Notes Due 2016
Carrying value and fair value of debt
Notes payable, carrying value	$ 62,000	62,000
Stated interest rate	7.31%
Debt intsruments maturity date	2016-03
Debt instrument issuance date	2009
Notes Due 2016 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 62,000	64,266
Notes Due 2017
Carrying value and fair value of debt
Notes payable, carrying value	$ 116,000	116,000
Stated interest rate	4.98%
Debt intsruments maturity date	2017-01
Debt instrument issuance date	2010
Notes Due 2017 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 116,000	123,967
Notes Due March 2018
Carrying value and fair value of debt
Notes payable, carrying value	$ 200,000	200,000
Stated interest rate	5.92%
Debt intsruments maturity date	2018-03
Debt instrument issuance date	2008
Notes Due March 2018 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 200,000	224,025
Notes Due December 2018
Carrying value and fair value of debt
Notes payable, carrying value	$ 450,000	450,000
Stated interest rate	5.75%
Debt intsruments maturity date	2018-12
Debt instrument issuance date	2013
Notes Due December 2018 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 450,000	465,630
Notes Due March 2019
Carrying value and fair value of debt
Notes payable, carrying value	$ 173,000	173,000
Stated interest rate	7.77%
Debt intsruments maturity date	2019-03
Debt instrument issuance date	2009
Notes Due March 2019 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 173,000	204,854
Notes Due January 2020
Carrying value and fair value of debt
Notes payable, carrying value	$ 207,000	207,000
Stated interest rate	5.50%
Debt intsruments maturity date	2020-01
Debt instrument issuance date	2010
Notes Due January 2020 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 207,000	233,932
Notes Due October 2020
Carrying value and fair value of debt
Notes payable, carrying value	$ 315,000	315,000
Stated interest rate	4.51%
Debt intsruments maturity date	2020-10
Debt instrument issuance date	2010
Notes Due October 2020 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 315,000	337,528
Notes Due January 2022
Carrying value and fair value of debt
Notes payable, carrying value	$ 87,000	87,000
Stated interest rate	5.60%
Debt intsruments maturity date	2022-01
Debt instrument issuance date	2010
Notes Due January 2022 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 87,000	99,983
Notes Due October 2022
Carrying value and fair value of debt
Notes payable, carrying value	$ 35,000	35,000
Stated interest rate	4.66%
Debt intsruments maturity date	2022-10
Debt instrument issuance date	2010
Notes Due October 2022 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 35,000	38,225
Notes Due October 2024
Carrying value and fair value of debt
Notes payable, carrying value	$ 850,000	850,000
Stated interest rate	6.125%
Debt intsruments maturity date	2024-10
Debt instrument issuance date	2014
Notes Due October 2024 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 850,000	893,325
Notes Due January 2025
Carrying value and fair value of debt
Notes payable, carrying value	$ 90,000	90,000
Stated interest rate	5.85%
Debt intsruments maturity date	2025-01
Debt instrument issuance date	2010
Notes Due January 2025 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 90,000	106,299
Notes Due October 2025
Carrying value and fair value of debt
Notes payable, carrying value	$ 175,000	175,000
Stated interest rate	4.91%
Debt intsruments maturity date	2025-10
Debt instrument issuance date	2010
Notes Due October 2025 \| Level 2
Carrying value and fair value of debt
Note payable, fair value	$ 175,000	193,665
Revolving credit facility
Carrying value and fair value of debt
Credit facility, carrying value	$ 999,000	999,000
Debt intsruments maturity date	2016-10
Revolving credit facility \| Level 2
Carrying value and fair value of debt
Credit facility, fair value	$ 999,000	$ 999,000

Date the debt instrument was issued, in CCYY format.

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM format.

+ References

No definition available.

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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

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Line-of-Credit Arrangement
-URI http://asc.fasb.org/extlink&oid=6517033

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Line-of-Credit Arrangement
-URI http://asc.fasb.org/extlink&oid=6517033

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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- Definition

Fair value portion of notes payable.

+ References

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