SECURITIES (Securities available for sale debt maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Due in 1 year or less	$ 12,487
Due in 1 to 5 years	19,354
Due in 5 to 10 years	238,253
Due after 10 years	1,560,562
Total debt securities	1,830,656
Mortgage and asset-backed securities	5,564,697
Equity securities with a readily determinable fair value	20,790	$ 19,629
Total investment securities	7,416,143
Estimated Fair Value
Due in 1 year or less	12,527
Due in 1 to 5 years	20,278
Due in 5 to 10 years	241,971
Due after 10 years	1,588,029
Total debt securities	1,862,805
Mortgage and asset-backed securities	5,566,341
Equity securities with a readily determinable fair value	20,790
Total investment securities	$ 7,449,936

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27198-111563