Fair Value - Fair Value Measurement (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed Gain/(Loss) From Loan Sale	$ (870)
Interest Rate Movement Effect	(2,133)
Servicing Rights Value	8,502
Security Price Change	325
Total Fair Value Measurement Gain/(Loss)	5,824	$ 4,186
Mortgage Banking: | Level 2 | Fair Value, Measurements, Recurring | Rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	490,184
Assumed Gain/(Loss) From Loan Sale	(666)
Interest Rate Movement Effect	(407)
Servicing Rights Value	4,641
Security Price Change	0
Total Fair Value Measurement Gain/(Loss)	3,568
Mortgage Banking: | Level 2 | Fair Value, Measurements, Recurring | Forward sales contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	705,405
Assumed Gain/(Loss) From Loan Sale	0
Interest Rate Movement Effect	0
Servicing Rights Value	0
Security Price Change	325
Total Fair Value Measurement Gain/(Loss)	325
Mortgage Banking: | Level 2 | Fair Value, Measurements, Recurring | Mortgages held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	350,558	357,912
Assumed Gain/(Loss) From Loan Sale	(204)
Interest Rate Movement Effect	(1,726)
Servicing Rights Value	3,861
Security Price Change	0
Total Fair Value Measurement Gain/(Loss)	$ 1,931	$ (5,954)