CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 390,606	$ 309,793	$ 261,428
Unrealized gains and losses on debt securities available for sale
Net gains (losses) arising during the period	27,845	39,262	(22,932)
Less reclassification adjustment for net (gains) losses included in net income	(377)	119	2,237
Total	27,468	39,381	(20,695)
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(2,251)	(989)	1,874
Less reclassification adjustment for net losses included in net income	2,074	1,291	2,494
Total	(177)	302	4,368
Defined benefit pension plan
Net losses arising during the period	(3,418)	(2,561)	(7,151)
Amortization of prior service (credit) cost	(98)	(93)	146
Amortization of actuarial net loss	721	188	447
Total	(2,795)	(2,466)	(6,558)
Other comprehensive income (loss), net	24,496	37,217	(22,885)
Total comprehensive income	$ 415,102	$ 347,010	$ 238,543