Fair Value - Fair Value Measurement (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed Gain/(Loss) From Loan Sale	$ 1,926
Interest Rate Movement Effect	(2,891)
Servicing Rights Value	12,312
Security Price Change	(1,509)
Total Fair Value Measurement Gain/(Loss)	9,838	$ 5,824
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rate Lock Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	778,931
Assumed Gain/(Loss) From Loan Sale	1,156
Interest Rate Movement Effect	42
Servicing Rights Value	8,126
Total Fair Value Measurement Gain/(Loss)	9,324
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Forward Sales Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	1,046,318
Security Price Change	(1,509)
Total Fair Value Measurement Gain/(Loss)	(1,509)
Mortgage Banking [Member] | Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgages Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional or Principal Amount	342,000	350,558
Assumed Gain/(Loss) From Loan Sale	770
Interest Rate Movement Effect	(2,933)
Servicing Rights Value	4,186
Total Fair Value Measurement Gain/(Loss)	$ 2,023	$ 1,931