CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 37,393	$ 52,703	$ 66,021	$ 98,542
Other comprehensive (loss) income, net of tax
Unrealized gain (loss) on debt securities arising during the period	24,290	24,510	22,427	48,015
Change in retirement obligation	353	246	681	536
Unrealized gain (loss) on derivatives	0	72	0	144
Other comprehensive income (loss)	24,643	24,828	23,108	48,695
Comprehensive income	$ 62,036	$ 77,531	$ 89,129	$ 147,237