Summary of Significant Accounting Policies New Accountings Pronouncements (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefits	$ 49,000
Additional Paid-in Capital | Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	285,000
Retained Earnings | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	1,323,000
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	$ 250,000