CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - UNAUDITED - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 30,317	$ 21,665
Investments available-for-sale:
Net change in unrealized gains on investments available-for-sale	8,814	(12,689)
Related income tax expense	(2,306)	3,321
Net investment gains reclassified into earnings	0	(63)
Related income tax expense	0	(16)
Net effect on other comprehensive income (loss) for the period	6,508	(9,415)
Defined benefit pension plan:
Recognition of unrealized gain (loss)	265	250
Related income tax (expense) benefit	(69)	(119)
Net effect on other comprehensive income for the period	196	131
Total other comprehensive income	6,704	(9,284)
Comprehensive income	$ 37,021	$ 12,381