Summary of Significant Accounting Policies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment - net unrealized gains on equity securities	$ 0
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
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