Annual report pursuant to Section 13 and 15(d)

HELD-TO-MATURITY SECURITIES - Schedule of Continuous Unrealized Loss Position (Details)

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HELD-TO-MATURITY SECURITIES - Schedule of Continuous Unrealized Loss Position (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value:    
Less Than Twelve Months, Fair Value $ 3,274,469 $ 4,118,300
Over Twelve Months, Fair Value 186,226 533,432
Fair Value 3,460,695 4,651,732
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss:    
Less than 12 Months, Unrealized Losses (35,221) (28,107)
Over 12 Months, Unrealized Losses (7,023) (12,307)
Unrealized Losses (42,244) (40,414)
Federal agencies: Mortgage-backed    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value:    
Less Than Twelve Months, Fair Value 2,855,360 3,692,890
Over Twelve Months, Fair Value 186,226 519,872
Fair Value 3,041,586 4,212,762
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss:    
Less than 12 Months, Unrealized Losses (31,470) (25,418)
Over 12 Months, Unrealized Losses (7,023) (12,086)
Unrealized Losses (38,493) (37,504)
Federal agencies: Other agencies    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value:    
Less Than Twelve Months, Fair Value 413,207 425,410
Over Twelve Months, Fair Value 0 6,647
Fair Value 413,207 432,057
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss:    
Less than 12 Months, Unrealized Losses (3,482) (2,689)
Over 12 Months, Unrealized Losses 0 (97)
Unrealized Losses (3,482) (2,786)
Total U.S. Government backed agencies    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value:    
Less Than Twelve Months, Fair Value 3,268,567 4,118,300
Over Twelve Months, Fair Value 186,226 526,519
Fair Value 3,454,793 4,644,819
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss:    
Less than 12 Months, Unrealized Losses (34,952) (28,107)
Over 12 Months, Unrealized Losses (7,023) (12,183)
Unrealized Losses (41,975) (40,290)
Municipal securities    
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value:    
Less Than Twelve Months, Fair Value 5,902 0
Over Twelve Months, Fair Value 0 6,913
Fair Value 5,902 6,913
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss:    
Less than 12 Months, Unrealized Losses (269) 0
Over 12 Months, Unrealized Losses 0 (124)
Unrealized Losses $ (269) $ (124)