FAIR VALUE MEASUREMENTS - Additional Information on Non-Recurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 2.7
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0		$ 0.0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0		0.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	44.0		45.0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	5.0		15.0
Other real estate owned	2.0		5.0
Fair Value, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0.0		0.0
Other real estate owned	0.0		0.0
Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0.0		0.0
Other real estate owned	0.0		0.0
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	5.0		15.0
Other real estate owned	2.0		5.0
SBA-Guaranteed Loan Servicing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	4.0	$ 4.0	4.0	$ 5.0	$ 5.0	$ 5.0
SBA-Guaranteed Loan Servicing [Member] | Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	4.0		4.0
SBA-Guaranteed Loan Servicing [Member] | Fair Value, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0		0.0
SBA-Guaranteed Loan Servicing [Member] | Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0		0.0
SBA-Guaranteed Loan Servicing [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	4.0		4.0
Mortgage Servicing Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	39.8	$ 40.3	$ 41.1	$ 38.6	$ 36.4	$ 32.4
Mortgage Servicing Rights [Member] | Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	25.0
Mortgage Servicing Rights [Member] | Fair Value, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0
Mortgage Servicing Rights [Member] | Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	0.0
Mortgage Servicing Rights [Member] | Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan servicing rights, fair value	$ 25.0