Summary of Significant Accounting Policies - ASU 2017-07 (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Labor and Related Expense \| Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net periodic benefit cost/(credit) reclassified	$ (1,946)	$ 843

Represents the quantification of the effect of adopting the new accounting standard or change in accounting principle expected by the entity to have a significant effect on the entity's financial statements.

No definition available.

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleEffectOfAdoptionQuantification
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration