Recently Issued Accounting Standards (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification from accumulated other comprehensive income to retained earnings	$ 200,000			$ 200,000
Corporate federal tax rate		21.00%	35.00%	21.00%	35.00%	35.00%
Minimum | Accounting Standards Update 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right of use asset and related lease liability				$ 90,000,000
Maximum | Accounting Standards Update 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right of use asset and related lease liability				$ 110,000,000