Borrowings - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Short Term And Long Term Debt [Line Items]
FHLB advances	$ 837.8
Unencumbered securities	123.0
Multifamily loans held as collateral	$ 798.6
Repurchase agreements
Schedule Of Short Term And Long Term Debt [Line Items]
Weighted average interest rate	3.19%	2.77%
Maturity in the first quarter	$ 4.0	$ 51.0
Maturity in more than 90 days	4.0	12.0
Repurchase agreements | Mortgage Backed Securities
Schedule Of Short Term And Long Term Debt [Line Items]
Mortgage-backed securities amortized cost	13.7	69.1
Mortgage-backed securities held for sale fair value	$ 13.9	$ 70.7
Repurchase agreements | Maturity over 90 days
Schedule Of Short Term And Long Term Debt [Line Items]
Maturity period	90 days