Summary of Significant Accounting Policies, Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Standards Update 2016-09 [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment			$ 0
Cumulative impact on opening retained earnings		$ 13,000
Accounting Standards Update 2016-09 [Member] | Retained Earnings [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment			(2,800)
Accounting Standards Update 2016-09 [Member] | Additional Paid-in Capital [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment			$ 2,800
Accounting Standards Update 2018-02 [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment		(1,681)
Cumulative impact on opening retained earnings	$ 1,700
Accounting Standards Update 2018-02 [Member] | Retained Earnings [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment		(1,681)
Accounting Standards Update 2018-02 [Member] | Additional Paid-in Capital [Member]
Accounting Pronouncements [Abstract]
Cumulative adjustment		$ 0