DISCLOSURES ABOUT FAIR VALUE OF FINANCIAL INSTRUMENTS - Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial Assets:
Available-for-sale securities, at fair value	$ 705,539	$ 274,619
Level 1
Financial Assets:
Available-for-sale securities, at fair value		112,881
Level 2
Financial Assets:
Available-for-sale securities, at fair value	705,539	161,738
Recurring
Financial Assets:
Available-for-sale securities, at fair value	705,539	274,619
Recurring | Level 1
Financial Assets:
Available-for-sale securities, at fair value	0	112,881
Recurring | Level 2
Financial Assets:
Available-for-sale securities, at fair value	705,539	161,738
Correspondent | Recurring | Interest Rate Swaps
Financial Assets:
Derivative asset	1,326	698
Financial Liabilities:
Derivative liability	448	1,389
Correspondent | Recurring | Interest Rate Caps
Financial Assets:
Derivative asset	75	5
Correspondent | Recurring | Level 2 | Interest Rate Swaps
Financial Assets:
Derivative asset	1,326	698
Financial Liabilities:
Derivative liability	448	1,389
Correspondent | Recurring | Level 2 | Interest Rate Caps
Financial Assets:
Derivative asset	75	5
Customer | Recurring | Interest Rate Swaps
Financial Assets:
Derivative asset	423	1,307
Financial Liabilities:
Derivative liability	1,325	698
Customer | Recurring | Interest Rate Caps
Financial Liabilities:
Derivative liability	75	5
Customer | Recurring | Level 2 | Interest Rate Swaps
Financial Assets:
Derivative asset	423	1,307
Financial Liabilities:
Derivative liability	1,325	698
Customer | Recurring | Level 2 | Interest Rate Caps
Financial Liabilities:
Derivative liability	$ 75	$ 5