CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 56,976	$ 44,642	$ 189,703	$ 40,291
Investments available-for-sale:
Net change in unrealized gains/ (losses) on investments available-for-sale	(8,183)	3,445	(27,149)	29,074
Related income tax expense/ (benefit)	2,073	(909)	6,931	(7,424)
Net investment gains reclassified into earnings	(49)	(51)	(178)	(432)
Related income tax expense	12	13	45	110
Net effect on other comprehensive income/ (loss)	(6,147)	2,498	(20,351)	21,328
Defined benefit pension plan:
Net change of unrealized loss	228	219	682	656
Related income tax benefit	(41)	(48)	(162)	(159)
Net effect on other comprehensive income/ (loss)	187	171	520	497
Total other comprehensive income/ (loss)	(5,960)	2,669	(19,831)	21,825
Comprehensive income	$ 51,016	$ 47,311	$ 169,872	$ 62,116