Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Available-for-sale securities, amortized cost	$ 13,894,348	$ 7,862,311
Held-to-maturity securities	$ 14,115,272	$ 15,188,236
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	350,000	0
Preferred stock, shares outstanding	350,000	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares, issued	51,655,607	52,586,498
Common stock, shares outstanding	51,655,607	52,586,498