CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Marketable securities available-for-sale, amortized cost	$ 749,703	$ 815,495
Marketable securities held-to-maturity, fair value	$ 17,968	$ 18,223
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	106,933,483	106,859,088
Common stock, shares outstanding (in shares)	106,933,483	106,859,088