Investment Securities (Narrative) (Details)
3 Months Ended
Mar. 31, 2020
USD ($)
security
Mar. 31, 2019
USD ($)
Dec. 31, 2019
USD ($)
security
Investment Securities      
Investment securities available-for-sale $ 761,539,000   $ 498,995,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) 21,600,000   2,800,000
Debt securities, available-for-sale, unrealized loss position $ 58,838,000   $ 205,599,000
Percentage of securities in unrealized loss positions, available-for-sale securities 7.70%   41.20%
Debt securities, available-for-sale, unrealized loss position, accumulated loss $ 312,000   $ 1,768,000
Investment securities held to maturity, fair value 0   87,561,000
Net unrealized gain (loss), held-to-maturity securities     800,000
Fair value     $ 22,341,000
Percentage of securities in unrealized loss positions, held-to-maturity securities     25.50%
Gross unrealized losses     $ 154,000
Equity securities held-for-trading $ 2,558,000   3,581,000
Number of days past due to be placed in nonaccrual status 90 days    
Estimated fair value of debt securities have right to call or prepay the obligations $ 97,900,000   37,600,000
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities within one year 3,000,000.0   3,000,000.0
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities of after one year through five years 19,800,000   34,600,000
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities after five years through ten years 46,400,000   0
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities of which is after 10 years 28,700,000    
Sales of trading securities 86,435,000 $ 0  
Debt Securities, Available-For-Sale      
Investment Securities      
Accrued interest receivable 2,400,000   2,000,000.0
US Government Sponsored Enterprises Debt Securities Excluding Specified Securities      
Investment Securities      
Investment securities available-for-sale 12,900,000   17,400,000
GSE debentures      
Investment Securities      
Investment securities available-for-sale 237,817,000   185,803,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 6,000,000.0   2,900,000
Investment securities held to maturity, fair value     31,290,000
Gross unrealized losses     $ 51,000
AFS number of positions | security 73   60
Number of securities in unrealized loss positions | security 4   5
Purchases of securities available-for-sale $ 75,200,000 0  
Number of securities transferred | security 9    
Amount of transfer $ 25,500,000    
GSE CMOs      
Investment Securities      
Investment securities available-for-sale 63,500,000   $ 85,900,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 1,100,000   $ (1,100,000)
AFS number of positions | security 33   61
Number of securities in unrealized loss positions | security 1   45
Purchases of securities available-for-sale $ 0 0  
GSE mortgage-related securities      
Investment Securities      
Investment securities available-for-sale 328,500,000   $ 153,300,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 9,400,000   $ 300,000
AFS number of positions | security 135   150
Number of securities in unrealized loss positions | security 22   48
Purchases of securities available-for-sale $ 176,900,000 0  
Number of securities transferred | security 8    
Amount of transfer $ 9,000,000.0    
SBA commercial loan asset-backed securities      
Investment Securities      
Investment securities available-for-sale $ 1,000   $ 34,000.0
AFS number of positions | security 1   4
Number of securities in unrealized loss positions | security 0   3
Purchases of securities available-for-sale $ 0 0  
Corporate debt obligations      
Investment Securities      
Investment securities available-for-sale 25,959,000   $ 28,986,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 600,000   $ 500,000
AFS number of positions | security 7   8
Number of securities in unrealized loss positions | security 0   0
Purchases of securities available-for-sale $ 0 0  
Number of securities transferred | security 1    
Amount of transfer $ 500,000    
U.S. Treasury bonds      
Investment Securities      
Investment securities available-for-sale 59,600,000   $ 44,900,000
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 3,900,000   $ 200,000
AFS number of positions | security 12   9
Number of securities in unrealized loss positions | security     5
Purchases of securities available-for-sale $ 0 $ 21,200,000  
Municipal obligations      
Investment Securities      
Investment securities available-for-sale 45,618,000    
Debt securities, available-for-sale, accumulated gross unrealized gain (loss) $ 600,000    
Investment securities held to maturity, fair value     $ 46,514,000
Gross unrealized losses     0
AFS number of positions | security 93    
Number of securities in unrealized loss positions | security 9    
Number of securities transferred | security 93    
Amount of transfer $ 47,700,000    
Collateral Pledged      
Investment Securities      
Investment securities pledged as collateral 489,300,000   433,600,000
Outstanding borrowings $ 0   $ 0