Assets and Liabilities Measured at Fair Value - Quantitative information about Level 3 measurements for fair value on a recurring basis (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities available-for-sale	$ 2,628,467	$ 2,615,850
Derivative assets	24,705	22,721
Derivative liabilities	26,433	25,376
Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Servicing rights for SBA/USDA loans	7,510	7,740
Residential mortgage servicing rights	11,877	8,262
Derivative assets	24,705	22,721
Derivative liabilities	26,433	25,376
Recurring | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Servicing rights for SBA/USDA loans	7,510	7,740
Residential mortgage servicing rights	11,877	8,262
Derivative assets	11,841	12,207
Derivative liabilities	15,732	16,744
Recurring | Level 3 | Servicing rights for SBA/USDA loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Servicing rights for SBA/USDA loans	$ 7,510	$ 7,740
Valuation technique	Discounted cash flow
Recurring | Level 3 | Servicing rights for SBA/USDA loans | Discount Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Servicing rights for SBA/USDA loans, measurement input	0.145	0.125
Recurring | Level 3 | Servicing rights for SBA/USDA loans | Prepayment Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Servicing rights for SBA/USDA loans, measurement input	0.121	0.083
Recurring | Level 3 | Residential mortgage servicing rights
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Residential mortgage servicing rights	$ 11,877	$ 8,262
Valuation technique	Discounted cash flow
Recurring | Level 3 | Residential mortgage servicing rights | Discount Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Residential mortgage servicing rights, measurement input	0.100	0.100
Recurring | Level 3 | Residential mortgage servicing rights | Prepayment Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Residential mortgage servicing rights, measurement input	0.106	0.095
Recurring | Level 3 | Corporate bonds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Debt securities available-for-sale	$ 995	$ 900
Valuation technique	Indicative bid provided by a broker
Recurring | Level 3 | Derivative assets - mortgage
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative assets	$ 1,190	$ 1,150
Valuation technique	Internal model
Recurring | Level 3 | Derivative assets - mortgage | Pull Through Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative assets, measurement input	0.807	0.800
Recurring | Level 3 | Derivative assets - other
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative assets	$ 10,651	$ 11,057
Valuation technique	Dealer priced
Recurring | Level 3 | Derivative liabilities - risk participations
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative liabilities	$ 8	$ 20
Valuation technique	Internal model
Recurring | Level 3 | Derivative liabilities - risk participations | Probable Exposure Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative liabilities, measurement input	0.004	0.004
Recurring | Level 3 | Derivative liabilities - risk participations | Probability of Default Rate | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative liabilities, measurement input	0.018	0.018
Recurring | Level 3 | Derivative liabilities - other
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative liabilities	$ 15,724	$ 16,724
Valuation technique	Dealer priced