Commitments and Credit Risk - Textual (Details) - USD ($)	3 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Outstanding letters of credit	$ 34,518,000	$ 47,621,000
Standby Letters of Credit
Other Commitments [Line Items]
Deferred revenue	$ 0	0
Minimum
Other Commitments [Line Items]
Term of letter of credit	9 months
Maximum
Other Commitments [Line Items]
Term of letter of credit	15 years
Credit card commitments
Other Commitments [Line Items]
Outstanding commitments	$ 568,117,000	564,592,000
Other loan commitments
Other Commitments [Line Items]
Outstanding commitments	$ 3,430,361,000	$ 3,086,696,000