Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of tax effects resulting from the TCJA	$ 0
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment - net unrealized gains on equity securities	6,500	$ 0
Taxes on cumulative effect adjustment	1,700
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of tax effects resulting from the TCJA	$ 1,300