Summary of Significant Accounting Policies - Carrying Value and Estimated Fair Value of Debt (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Carrying value and estimated fair value of debt
Credit agreement, carrying value	$ 148,125us-gaap_LoansPayable	$ 120,000us-gaap_LoansPayable
Convertible debt, carrying value	150,000us-gaap_ConvertibleDebt	150,000us-gaap_ConvertibleDebt
Credit agreement, fair value	148,125us-gaap_LoansPayableFairValueDisclosure	120,000us-gaap_LoansPayableFairValueDisclosure
Convertible debt, fair value	$ 203,880	$ 178,920

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16(a)(2))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

+ Details

Name:	us-gaap_ConvertibleDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Convertible Security

-URI http://asc.fasb.org/extlink&oid=6509036

+ Details

Name:	us-gaap_ConvertibleDebtFairValueDisclosures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, aggregate carrying value as of the balance sheet date of loans payable (with maturities initially due after one year or beyond the operating cycle if longer).

+ 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 210.9-03.16)

-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

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16(a)(2))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

+ Details

Name:	us-gaap_LoansPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of contractual obligation to pay money on demand or on fixed or determinable dates.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansPayableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant