CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Available-for-sale securities, Amortized cost	$ 2,375,637	$ 2,345,791
Allowance for credit losses	$ 0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	133,115,699	132,984,756
Common Stock, Shares, Outstanding	125,897,827	127,597,569
Treasury stock, shares outstanding	7,217,872	5,387,187