BORROWINGS - Summary of Short-Term and Long-Term Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Short-term borrowings:
FHLB advances maturing within one year	$ 764,600,000	$ 375,500,000
Long-term debt:
FHLB advances maturing beyond one year	51,356,000	118,942,000
Subordinated term loan due 2018	7,279,000	7,166,000
Capital lease obligations and other debt	5,521,000	5,752,000
Long-term debt	159,424,000	194,967,000
Short-term borrowings	764,600,000	375,500,000
Revolving Credit Facility
Long-term debt:
Line of credit facility	0
Line of credit outstanding borrowing capacity	$ 15,000,000
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Long-term debt:
Debt instrument, basis spread on variable rate	4.00%
Federal Funds Line of Credit
Long-term debt:
Loans pledged as collateral	$ 1,195,326,000
Federal Reserve Bank's Discount Window
Long-term debt:
Long-term debt	0
Federal Funds Purchased | Federal Funds Line of Credit
Long-term debt:
Short-term borrowings	210,000,000
Line of credit amounts outstanding	0	0
Subordinated notes due 2023
Long-term debt:
Subordinated notes	38,050,000	38,050,000
Subordinated notes due 2024
Long-term debt:
Subordinated notes		0
Maturing October 7, 2033
Long-term debt:
Junior subordinated debt to unconsolidated trusts:	5,885,000	5,701,000
Maturing December 15, 2033
Long-term debt:
Junior subordinated debt to unconsolidated trusts:	6,997,000	6,853,000
Maturing September 30, 2035
Long-term debt:
Junior subordinated debt to unconsolidated trusts:	15,371,000	0
Maturing December 15, 2037
Long-term debt:
Junior subordinated debt to unconsolidated trusts:	12,904,000	12,503,000
Federal Reserve Bank's Discount Window
Long-term debt:
Loans pledged as collateral	$ 4,903,000
Federal Reserve Bank's Discount Window | Minimum
Long-term debt:
Percentage of collateral that may be borrowed (as a percent)	60.00%
Federal Reserve Bank's Discount Window | Maximum
Long-term debt:
Percentage of collateral that may be borrowed (as a percent)	65.00%
Federal Reserve Bank's Discount Window | Federal Funds Line of Credit
Long-term debt:
Long-term debt		$ 0