Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.P.3)
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747

Name:	us-gaap_SeveranceCosts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Chief Executive Officer Retirement (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Retirement severance expense		$ 0	$ 0	$ 18,578
Employee Severance [Member] \| Expected Cash Payment [Member] \| Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Retirement severance expense				11,800
Employee Severance [Member] \| Taxes and Other Expenses [Member] \| Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Retirement severance expense				400
Nonvested Shares [Member] \| Employee Severance [Member] \| Accelerated Vesting of Shares [Member] \| Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Retirement severance expense				$ 5,000
Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number				113,900
Stock Options [Member] \| Employee Severance [Member] \| Accelerated Vesting of Shares [Member] \| Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Retirement severance expense	$ 1,400			$ 1,400
Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number				101,640