Derivative Instruments and Hedging Activities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018	Apr. 01, 2010
Debt Instrument, Redemption, Period One \| Mortgage Loan On Headquarters Facility \| Mortgage loan
Schedule of interest rate derivatives designated as cash flow hedges of interest rate risk
Strike rate		5.91%	5.91%
Debt Instrument, Redemption, Period Two \| Mortgage Loan On Headquarters Facility \| Mortgage loan
Schedule of interest rate derivatives designated as cash flow hedges of interest rate risk
Strike rate		6.07%	6.07%
Interest rate swap \| First half of mortgage
Schedule of interest rate derivatives designated as cash flow hedges of interest rate risk
Notional	$ 1,275	$ 1,299
Asset (Liability)	$ (1)	$ (5)
Effective Date	Apr. 01, 2010	Apr. 01, 2010
Maturity Date	Apr. 01, 2019	Apr. 01, 2019
Derivative, Type of Interest Rate Paid on Swap	1-month LIBOR	1-month LIBOR
Strike rate	5.90%
Interest rate swap \| Second half of mortgage
Schedule of interest rate derivatives designated as cash flow hedges of interest rate risk
Notional	$ 1,275	$ 1,299
Asset (Liability)	$ (2)	$ (6)
Effective Date	Apr. 01, 2010	Apr. 01, 2010
Maturity Date	Apr. 01, 2019	Apr. 01, 2019
Derivative, Type of Interest Rate Paid on Swap	1-month LIBOR	1-month LIBOR
Strike rate	6.10%

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

When the derivative or group of derivatives presented is a swap, the type of interest rate (fixed, variable, stepped, etc.) paid on the swap.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column A
-Footnote 1

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

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- Definition

Date the entity entered into the derivative contract, in CCYY-MM-DD format.

+ References

No definition available.

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- Definition

Date the derivative contract matures, in CCYY-MM-DD format.

+ References

No definition available.

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