Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Or Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	$ 3,864,707	$ 3,865,447	$ 3,890,652	$ 3,676,544
Other comprehensive income (loss) before reclassification:
Unrealized gains (losses)	(19,131)	(1,446)	5,061	441
Reclassifications from other comprehensive income (loss) to net income:
Total other comprehensive income (loss)	(18,962)	(1,446)	5,230	441
Balance at the end of the period	4,134,709	3,896,486	4,134,709	3,896,486
Total AOCI [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	(94,779)	(82,383)	(118,971)	(84,270)
Other comprehensive income (loss) before reclassification:
Unrealized gains (losses)	(19,131)	(1,446)	5,061	441
Impact of settlements - defined benefit pension plan	169		169
Reclassifications from other comprehensive income (loss) to net income:
Total other comprehensive income (loss)	(18,962)	(1,446)	5,230	441
Balance at the end of the period	(113,741)	(83,829)	(113,741)	(83,829)
Net Unrealized Gain (Loss) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	(94,752)	(82,556)	(118,944)	(84,443)
Other comprehensive income (loss) before reclassification:
Unrealized gains (losses)	(19,131)	(1,446)	5,061	441
Reclassifications from other comprehensive income (loss) to net income:
Total other comprehensive income (loss)	(19,131)	(1,446)	5,061	441
Balance at the end of the period	(113,883)	(84,002)	(113,883)	(84,002)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Balance at the beginning of the period	(27)	173	(27)	173
Other comprehensive income (loss) before reclassification:
Impact of settlements - defined benefit pension plan	169		169
Reclassifications from other comprehensive income (loss) to net income:
Total other comprehensive income (loss)	169	0	169	0
Balance at the end of the period	$ 142	$ 173	$ 142	$ 173