Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-02.14)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 14

-Article 5

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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

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- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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-Publisher FASB

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-Topic 210

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 13

-Subparagraph a

-Article 5

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-Name Regulation S-X (SX)

-Number 210

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Summary of Significant Accounting Policies (Details 8) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property and Equipment
Depreciation expense	$ 68,300,000us-gaap_Depreciation	$ 61,400,000us-gaap_Depreciation	$ 50,800,000us-gaap_Depreciation
Property and equipment, gross	585,613,000us-gaap_PropertyPlantAndEquipmentGross	526,499,000us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation	(413,697,000)	(354,166,000)
Property and equipment, net	171,916,000us-gaap_PropertyPlantAndEquipmentNet	172,333,000us-gaap_PropertyPlantAndEquipmentNet
Building improvements
Property and Equipment
Property and equipment, gross	13,416,000	12,074,000
Building improvements \| Minimum
Property and Equipment
Estimated useful lives of assets	2 years
Building improvements \| Maximum
Property and Equipment
Estimated useful lives of assets	10 years
Equipment
Property and Equipment
Property and equipment, gross	185,391,000	180,540,000
Equipment \| Minimum
Property and Equipment
Estimated useful lives of assets	3 years
Equipment \| Maximum
Property and Equipment
Estimated useful lives of assets	15 years
Capital leases - property
Property and Equipment
Property and equipment, gross	26,945,000	26,945,000
Capital leases - equipment
Property and Equipment
Property and equipment, gross	7,883,000	2,794,000
Capitalized internal-use software
Property and Equipment
Depreciation expense	40,900,000	34,800,000	28,800,000
Property and equipment, gross	351,978,000	304,146,000
Property and equipment, net	$ 85,600,000	$ 78,800,000
Capitalized internal-use software \| Minimum
Property and Equipment
Estimated useful lives of assets	3 years
Capitalized internal-use software \| Maximum
Property and Equipment
Estimated useful lives of assets	5 years