Income Taxes - Reconciliation between Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	35.00%	35.00%
State income taxes, net of the federal tax effect	7.20%	5.80%	5.90%
Net deferred tax assets revaluation (TCJ Act)	0.00%	4.30%	0.00%
Meals and entertainment	0.30%	0.30%	0.40%
Disallowed officer's compensation	0.20%	0.10%	0.10%
FDIC premiums	0.50%	0.00%	0.00%
Share-based compensation expense on incentive stock options and ESPP	(1.40%)	(2.10%)	0.00%
Qualified affordable housing project tax credits	(0.30%)	(0.40%)	(0.50%)
Tax-exempt interest income	(0.60%)	(0.30%)	(0.20%)
Valuation allowance benefit	0.00%	0.00%	(0.30%)
Other, net	(0.40%)	(0.70%)	(0.90%)
Effective income tax rate	26.50%	42.00%	39.50%