Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Investment securities:
Estimated fair value	$ 71.1	$ 94.5
Stockholders' equity:
Nonvoting, noncumulative preferred stock, shares authorized (in shares)	100,000	100,000
Nonvoting, noncumulative preferred stock, shares issued (in shares)	0	0
Nonvoting, noncumulative preferred stock, shares outstanding (in shares)	0	0

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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