Consolidated Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 25,655	$ 13,171	$ 32,230	$ 36,852
Other comprehensive income (loss):
Unrealized gains (losses) on securities available for sale	720	1,192	13,338	9,084
Reclassification adjustment for securities gains included in net income	(1,466)	(11)	(1,464)	(11)
Income tax effect	158	(247)	(2,493)	(1,906)
Net of tax amount	(588)	934	9,381	7,167
Change in unrealized gain/(loss) on postretirement benefit:
Reclassification adjustment for deferred tax on defined benefit postretirement medical plan				82
Net of tax amount				82
Total other comprehensive income (loss)	(588)	934	9,381	7,249
Comprehensive income	$ 25,067	$ 14,105	$ 41,611	$ 44,101