The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of investments, not including unrealized gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, held at each balance sheet date and included in earnings for the period.

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=98514028&loc=d3e3602-108585

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

Employee Benefit Plan - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
Employee Benefit Plan - (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2014	Dec. 31, 2016
Retirement Benefits [Abstract]
Assets contributed to 401(k) Plan					$ 7,900
Restricted investments	$ 4,462		$ 4,462			$ 5,636
401(k) Plan distribution period (in years)			4 years
Compensation expense for assets allocated to participants			$ 1,200	$ 1,400
Gain on allocated asset (less than)	$ 100	$ 100	$ 100	$ 100