New Authoritative Accounting Guidance (Details) - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2017
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment that reduced retained earnings		$ 15.4
Scenario, Forecast | Minimum | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of use assets	$ 200.0
Lease obligations	$ 230.0
Total risk-based capital	0.10%
Tier 1 capital	0.07%
Scenario, Forecast | Maximum | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of use assets	$ 250.0
Lease obligations	$ 280.0
Total risk-based capital	0.12%
Tier 1 capital	0.09%