PARENT COMPANY STATEMENTS, Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Expenses [Abstract]
Interest on borrowings	$ 3,898	$ 4,677	$ 3,904
Acquisition expenses	8,608	(769)	25,986
Loss on debt prepayment	0	318	0
Other expenses	24,090	21,471	22,609
Income before tax benefit and equity in undistributed net income of subsidiaries	209,338	212,988	159,965
Income tax benefit	(40,275)	(44,347)	(9,248)
Net income	169,063	168,641	150,717
Other comprehensive income/(loss), net of tax [Abstract]
Changes in other comprehensive (loss)/income related to pension and other post retirement obligations	(2,045)	(11,204)	168
Changes in other comprehensive income/(loss) related to unrealized losses on available-for-sale securities	37,124	(30,402)	(11,065)
Other comprehensive income/(loss)	35,079	(41,398)	(10,897)
Comprehensive income	204,142	127,035	139,820
Parent Company [Member]
Dividends from subsidiaries [Abstract]
Bank subsidiary	115,000	98,000	91,000
Non-bank subsidiaries	27,600	9,250	35,500
Interest and dividends on investments	134	161	133
Total revenues	142,734	107,411	126,633
Expenses [Abstract]
Interest on borrowings	4,244	4,677	3,904
Acquisition expenses	1,248	0	91
Loss on debt prepayment	0	318	0
Other expenses	477	131	26
Total expenses	5,969	5,126	4,021
Income before tax benefit and equity in undistributed net income of subsidiaries	136,765	102,285	122,612
Income tax benefit	4,545	1,330	1,930
Income before equity in undistributed net income of subsidiaries	141,310	103,615	124,542
Equity in undistributed net income of subsidiaries	27,753	65,026	26,175
Net income	169,063	168,641	150,717
Other comprehensive income/(loss), net of tax [Abstract]
Changes in other comprehensive (loss)/income related to pension and other post retirement obligations	(2,045)	(11,204)	168
Changes in other comprehensive income/(loss) related to unrealized losses on available-for-sale securities	37,124	(30,402)	(11,065)
Other comprehensive income/(loss)	35,079	(41,606)	(10,897)
Comprehensive income	$ 204,142	$ 127,035	$ 139,820