Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 5,853	$ 8,997	$ 20,144	$ 26,191
Change in unrealized gain (loss) on investments:
Net unrealized gain (loss) arising during the period	447	35	4,777	(2,658)
Other-than-temporary impairment loss charged to income	0	0	0	80
Call and repayment losses charged to investment income	(2)	(19)	(1)	(15)
Reclassification adjustment for net realized loss (gain)	(26)	(71)	(59)	(732)
Net change in unrealized gain (loss)	419	(55)	4,717	(3,325)
Deferred income taxes on above change	(83)	13	(1,173)	842
Total other comprehensive income (loss), net of income taxes	336	(42)	3,544	(2,483)
Comprehensive income	$ 6,189	$ 8,955	$ 23,688	$ 23,708