Commitments and Credit Risk (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Total commitments	$ 1,444,875	$ 1,546,495
Financing Receivable | Portfolio Segment Concentration Risk | Energy
Loss Contingencies [Line Items]
Concentration of credit risk	10.00%
Financing Receivable | Portfolio Segment Concentration Risk | Energy | Oil and Gas, Exploration Loans
Loss Contingencies [Line Items]
Concentration of credit risk	65.00%
Financing Receivable | Portfolio Segment Concentration Risk | Energy | Oil and Natural, Production Loans
Loss Contingencies [Line Items]
Concentration of credit risk	35.00%
Commitments to originate loans
Loss Contingencies [Line Items]
Total commitments	$ 182,941	134,652
Standby letters of credit
Loss Contingencies [Line Items]
Total commitments	34,828	39,035
Lines of credit
Loss Contingencies [Line Items]
Total commitments	1,204,712	1,351,873
Future lease commitments
Loss Contingencies [Line Items]
Total commitments	$ 22,394	$ 20,935