CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
CONSOLIDATED BALANCE SHEETS
Amortized Cost	$ 5,985,031	$ 4,080,663
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	300,000,000	300,000,000
Common stock, issued (in shares)	140,191,133	139,917,150
Common stock outstanding (in shares)	129,912,272	129,928,479
Treasury stock (in shares)	10,278,861	9,988,671