CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 133,666	$ 154,323	$ 74,854
Net unrealized holding (losses)/gains on marketable securities:
Unrealized holding (losses)/gains, net of tax of $45,321, $10,333, and $(5,607), respectively	(151,888)	(28,873)	13,711
Reclassification adjustment for gains included in net income, net of tax of $0, $92, and $6, respectively	(1)	(287)	(15)
Net unrealized holding (losses)/gains on marketable securities	(151,889)	(29,160)	13,696
Change in fair value of interest rate swaps:
Unrealized holding losses on interest rate swaps, net of tax of $0, $0, and $209, respectively	0	0	(946)
Reclassification adjustment for losses included in net income, net of tax of $0, $0, and $(209), respectively	0	0	946
Net change in fair value of interest rate swaps	0	0	0
Defined benefit plan:
Net gain/(loss), net of tax $(7,182), $(9,144), $4,169, respectively	18,884	23,748	(11,301)
Reclassification adjustments for prior period service costs and actuarial (gains)/losses included in net income, net of tax of $202, $(515), and $(395), respectively	(524)	1,332	997
Net gain/(loss) on defined benefit plans	18,360	25,080	(10,304)
Other comprehensive (loss)/income	(133,529)	(4,080)	3,392
Total comprehensive income	$ 137	$ 150,243	$ 78,246