v3.8.0.1
Fair Value - Recorded Amounts of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale $ 519,364 $ 509,578
U.S. Treasury Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 493 297
Agency Mortgage-backed Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 464,019 468,909
Beneficial interest - FHLMC securitization    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 35,852 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 519,364 509,578
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 493 297
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 464,019 468,909
Fair Value on Recurring Basis | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 19,000  
Fair Value on Recurring Basis | Beneficial interest - FHLMC securitization    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 35,852 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 493 297
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 493 297
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 493 297
Fair Value Measurement Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 483,019 468,909
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 483,019 468,909
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 464,019 468,909
Fair Value Measurement Level 2 | Fair Value on Recurring Basis | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 19,000  
Fair Value Measurement Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale 35,852 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 35,852 40,372
Fair Value Measurement Level 3 | Fair Value on Recurring Basis | Beneficial interest - FHLMC securitization    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Investment securities available for sale $ 35,852 $ 40,372