Fair Value - Fair Value Measurement (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assumed Gain/(Loss) From Loan Sale	$ 7,114
Interest Rate Movement Effect	10,173
Servicing Rights Value	13,244
Security Price Change	(7,313)
Total Fair Value Measurement Gain/(Loss)	23,218		$ 14,309
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	801,302
Assumed Gain/(Loss) From Loan Sale	4,554
Interest Rate Movement Effect	5,514
Servicing Rights Value	8,220
Total Fair Value Measurement Gain/(Loss)	18,288
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	1,117,669
Security Price Change	(7,313)
Total Fair Value Measurement Gain/(Loss)	(7,313)
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	410,314		$ 447,444
Assumed Gain/(Loss) From Loan Sale	2,560
Interest Rate Movement Effect	4,659
Servicing Rights Value	5,024
Total Fair Value Measurement Gain/(Loss)	$ 12,243	$ 10,880