Significant Accounting Policies Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act	$ 9,535
Cumulative Effect of New Accounting Principle in Period of Adoption			$ (2,285)	$ 0
Gross interchange and debit card transaction fees	6,071
Gross cost related to interchange and debit card transactions	2,913	$ 3,223
Interchange and debit card transaction fees	$ 3,158	$ 5,574