UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized gains (losses) arising during the period, tax effect	$ (6,783)	$ 7,030
Reclassification adjustments for (gains) losses realized in net income, tax effect	(3)	3
Net unrealized gains(losses) arising during the period, tax effect	(11,112)	2,645
Reclassification adjustments for losses realized in net income, tax effect	$ (348)	$ (77)