SECURITIES (Available-for-sale Securities, Debt Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in 1 year or less	$ 3,579
Due in 1 to 5 years	26,507
Due in 5 to 10 years	168,981
Due after 10 years	1,536,370
Total debt securities	1,735,437
Mortgage and asset-backed securities	4,269,159
Equity securities with a readily determinable fair value	19,629	$ 18,435
Total investment securities	6,024,225
Estimated Fair Value
Due in 1 year or less	3,624
Due in 1 to 5 years	27,252
Due in 5 to 10 years	173,927
Due after 10 years	1,602,971
Total debt securities	1,807,774
Mortgage and asset-backed securities	4,300,572
Equity securities with a readily determinable fair value	19,629	$ 18,435
Total investment securities	$ 6,127,975

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