v3.8.0.1
Fair Value Measurements - Recorded Amounts of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale $ 471,502 $ 509,578
U.S. Treasury Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 495 297
Agency Mortgage-backed Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 432,448 468,909
Beneficial interest - FHLMC securitizations    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 38,559 40,372
Fair Value on Recurring Basis    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 471,502 509,578
Fair Value on Recurring Basis | U.S. Treasury Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 495 297
Fair Value on Recurring Basis | Agency Mortgage-backed Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 432,448 468,909
Fair Value on Recurring Basis | Beneficial interest - FHLMC securitizations    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 38,559 40,372
Fair Value Measurement Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 495 297
Fair Value Measurement Level 1 | Fair Value on Recurring Basis    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 495 297
Fair Value Measurement Level 1 | Fair Value on Recurring Basis | U.S. Treasury Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 495 297
Fair Value Measurement Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 432,448 468,909
Fair Value Measurement Level 2 | Fair Value on Recurring Basis    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 432,448 468,909
Fair Value Measurement Level 2 | Fair Value on Recurring Basis | Agency Mortgage-backed Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 432,448 468,909
Fair Value Measurement Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 38,559 40,372
Fair Value Measurement Level 3 | Fair Value on Recurring Basis    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 38,559 40,372
Fair Value Measurement Level 3 | Fair Value on Recurring Basis | Beneficial interest - FHLMC securitizations    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale $ 38,559 $ 40,372