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Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent
Federal statutory income tax rate		35.00%	35.00%	35.00%
California franchise tax, net of federal tax benefit		6.90%	6.80%	6.80%
Write down of federal deferred tax assets, net		10.50%	0.00%	0.00%
Tax exempt interest on municipal securities and loans		(6.10%)	(4.00%)	(4.20%)
Tax exempt earnings on bank owned life insurance		(1.00%)	(0.80%)	(1.00%)
Non-deductible acquisition related expenses		0.80%	0.00%	0.00%
Low income housing and qualified zone academy bond tax credits		(0.40%)	(0.30%)	(0.20%)
Stock-based compensation excess tax benefit		(0.30%)	0.00%	0.00%
Other		(0.80%)	(0.10%)	(0.10%)
Effective Tax Rate		44.60%	36.60%	36.30%
Write-down to net deferred tax assets recorded as income tax expense	$ 3.0	$ 3.0

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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