Organization and Summary of Significant Accounting Policies - VIEs and Cash and Due from Banks (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entities
Period over which affordable housing tax credits are recognized	10 years
Cash and Due from Banks
Average cash reserves required with Federal Reserve Bank	$ 52.5	$ 48.9	$ 38.0
Other liabilities | VIEs, not primary beneficiary
Variable Interest Entities
Unfunded commitments to fund low-income housing partnerships	$ 35.1