Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Amortized cost	$ 2,155,330	$ 2,255,874
Fair Value, Held-to-maturity	$ 842,050	$ 897,374
Common stock, par value
Common stock, authorized	225,000,000	225,000,000
Common stock, shares issued	110,157,384	108,251,981
Common stock, shares outstanding	110,157,384	108,251,981