Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Notes Payable (Term Loan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Unsecured term loan	$ 1,067,362	$ 1,098,764
Term Loan
Debt Instrument [Line Items]
Unsecured term loan	$ 250,000	$ 250,000
Term Loan \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.20%
Term Loan \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.20%
Term Loan \| LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.70%
Term Loan \| Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.50%
Term Loan \| One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.00%
Term Loan \| Base Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.00%
Term Loan \| Base Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.75%