Leadership Changes and Restructuring Activities - Rollforward of Estimated Fair Value Liability Established for Total Severance and Other Related Costs (Details) $ in Thousands	9 Months Ended
Sep. 30, 2017 USD ($)
Leadership Changes
Balance, January 1	$ 964
Accretion	17
Cash payments	(783)
Balance, September 30, 2017	$ 198

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866

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