CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 28,276	$ 24,399	$ 58,593	$ 46,064
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale	7,167	(4,230)	15,981	(16,919)
Related income tax expense	(1,873)	1,107	(4,179)	4,428
Net investment gains reclassified into earnings	(5)	0	(5)	(63)
Related income tax expense	1	0	1	16
Net effect on other comprehensive income (loss) for the period	5,290	(3,123)	11,798	(12,538)
Defined benefit pension plan:
Recognition of unrealized gain (loss)	265	250	530	500
Related income tax (expense) benefit	(70)	(65)	(139)	(184)
Net effect on other comprehensive income for the period	195	185	391	316
Total other comprehensive income	5,485	(2,938)	12,189	(12,222)
Comprehensive income	$ 33,761	$ 21,461	$ 70,782	$ 33,842