The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

Reference 1: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

Debt (Details) - USD ($) $ in Thousands	May 01, 2019	Mar. 31, 2019	Dec. 31, 2018
Revolving Credit Agreement [Line Items]
Line of credit facility		$ 140,000	$ 40,000
Senior Notes \| Senior Notes Due 2026
Revolving Credit Agreement [Line Items]
Long-term debt outstanding		1,050,000
Revolving Credit Facility \| Third Amended Credit Agreement
Revolving Credit Agreement [Line Items]
Line of credit facility		140,000
Letter of Credit
Revolving Credit Agreement [Line Items]
Outstanding letters of credit		13,600
Line of Credit \| San Mateo Credit Facility
Revolving Credit Agreement [Line Items]
Outstanding letters of credit		16,200
Long-term line of credit		$ 220,000
Subsequent Event \| Senior Notes \| Senior Notes Due 2026
Revolving Credit Agreement [Line Items]
Long-term debt outstanding	$ 1,050,000
Subsequent Event \| Revolving Credit Facility \| Third Amended Credit Agreement
Revolving Credit Agreement [Line Items]
Line of credit facility	190,000
Subsequent Event \| Letter of Credit
Revolving Credit Agreement [Line Items]
Outstanding letters of credit	$ 13,600