Marketable Securities and Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale marketable securities	$ 63,100,000
Cash collateral	38,700,000
Assets, fair value	66,914,000	$ 52,907,000
Realized gains or losses	$ 0	$ 0
Percentage of total fair value of available for sale securities in unrealized loss position	81.00%	59.00%
Unrealized Loss	$ 100,000
Transfers between Level I and Level II assets	0	$ 0
Level II
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	0	1,000
Carrying value of notes payable	499,600,000	544,900,000
Certificates of deposit
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	2,319,000	2,318,000
Certificates of deposit \| Level II
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	0	0
U.S. treasuries
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	64,091,000	50,082,000
U.S. treasuries \| Level II
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	$ 0	$ 0
U.S. treasuries \| Minimum
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Contractual maturities	1 year
U.S. treasuries \| Maximum
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Contractual maturities	4 years
Available-for-sale Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Available-for-sale marketable securities	$ 1,500,000

Available for sale securities contractual maturity period.

No definition available.

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- Definition

Available for sale securities unrealized loss position percentage of total fair value.

+ References

No definition available.

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

The carrying amount of securities categorized neither as held-to-maturity nor trading which serve as security for borrowings or other arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX210.4-08(b))
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-Publisher SEC
-Name Regulation S-X (SX)
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-Section 03
-Paragraph 6
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- Definition

Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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-Paragraph 1
-Subparagraph (SX 210.9-03.1)
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- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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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

Fair value portion of notes payable.

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-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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