SECURITIES - Schedule of Debt and Equity Securities Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
AVAILABLE FOR SALE:
Amortized cost	$ 2,013,485
Gross unrealized gain	10,554
Gross unrealized loss	34,603
Estimated fair value	1,989,436
Amortized cost		$ 1,541,967
Gross unrealized gains		9,163
Gross unrealized loss		12,375
Estimated fair value		1,538,755
HELD TO MATURITY:
Amortized cost	162,931	909,506
Gross unrealized gains	360	16,322
Gross unrealized losses	3,510	4,028
Estimated fair value	159,781	921,800
U.S. Government Agency Debentures
AVAILABLE FOR SALE:
Amortized cost		108,869
Gross unrealized gains		0
Gross unrealized loss		0
Estimated fair value		108,869
State and Political Subdivisions
AVAILABLE FOR SALE:
Amortized cost	728,142
Gross unrealized gain	6,115
Gross unrealized loss	17,656
Estimated fair value	716,601
Amortized cost		392,760
Gross unrealized gains		3,895
Gross unrealized loss		3,991
Estimated fair value		392,664
HELD TO MATURITY:
Amortized cost	3,083	413,632
Gross unrealized gains	5	10,879
Gross unrealized losses	42	2,583
Estimated fair value	3,046	421,928
Other Stocks and Bonds
AVAILABLE FOR SALE:
Amortized cost	3,000
Gross unrealized gain	0
Gross unrealized loss	291
Estimated fair value	2,709
Amortized cost		5,024
Gross unrealized gains		31
Gross unrealized loss		0
Estimated fair value		5,055
Other Equity Securities
AVAILABLE FOR SALE:
Amortized cost		6,027
Gross unrealized gains		0
Gross unrealized loss		107
Estimated fair value		5,920
Residential
AVAILABLE FOR SALE:
Amortized cost	738,585
Gross unrealized gain	3,498
Gross unrealized loss	9,111
Estimated fair value	732,972
Amortized cost		720,930
Gross unrealized gains		4,476
Gross unrealized loss		7,377
Estimated fair value		718,029
HELD TO MATURITY:
Amortized cost	59,655	129,044
Gross unrealized gains	154	1,631
Gross unrealized losses	1,140	239
Estimated fair value	58,669	130,436
Commercial
AVAILABLE FOR SALE:
Amortized cost	543,758
Gross unrealized gain	941
Gross unrealized loss	7,545
Estimated fair value	537,154
Amortized cost		308,357
Gross unrealized gains		761
Gross unrealized loss		900
Estimated fair value		308,218
HELD TO MATURITY:
Amortized cost	100,193	366,830
Gross unrealized gains	201	3,812
Gross unrealized losses	2,328	1,206
Estimated fair value	$ 98,066	$ 369,436

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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