Fair Values of Assets and Liabilities (Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Measure Both Recurring and Non-Recurring) (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) $ / Loan	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	$ 1,649,636	$ 1,724,667	$ 637,663
Loans held-for-investment	30,173		16,294
Derivative assets	49,703	56,394	101,052
Impaired loans—collateral based	$ 79,318	90,516	95,976
Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull-through rate	40.00%
Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull-through rate	100.00%
Other real estate owned, including covered other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraisal adjustment - cost of sale	10.00%
Municipal Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	$ 124,120	131,809	111,640
U.S. Government agencies
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	157,510	189,152	69,916
Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loans held-for-investment	30,173	22,137	16,294
MSRs	27,307	19,103	13,382
Derivative assets	49,703	56,394	101,052
Fair Value, Measurements, Recurring | Municipal Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	124,120	131,809	111,640
Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	157,510	189,152	69,916
Fair Value, Measurements, Nonrecurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans—collateral based	57,259
Other real estate owned, including covered other real estate owned	42,617
Level 3 | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loans held-for-investment	30,173	22,137	0
MSRs	27,307	19,103	13,382
Derivative assets	$ 1,047	2,291	9,731
Level 3 | Fair Value, Measurements, Recurring | Loans held-for- investment
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Constant prepayment rate (CPR)	9.42%
Level 3 | Fair Value, Measurements, Recurring | Loans held-for- investment | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	3.70%
Credit loss rate	0.89%
Level 3 | Fair Value, Measurements, Recurring | Loans held-for- investment | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	3.00%
Credit loss rate	0.00%
Level 3 | Fair Value, Measurements, Recurring | Loans held-for- investment | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	4.00%
Credit loss rate	3.00%
Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	9.81%
Constant prepayment rate (CPR)	9.64%
Cost of servicing (in dollars per loan) | $ / Loan	65
Cost of servicing - delinquent (in dollars per loan) | $ / Loan	422
Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	9.00%
Constant prepayment rate (CPR)	0.00%
Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	16.00%
Constant prepayment rate (CPR)	34.00%
Level 3 | Fair Value, Measurements, Recurring | Municipal Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	$ 77,341	79,626	69,812
Level 3 | Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Available-for-sale securities	4,110	$ 0	$ 0
Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Impaired loans—collateral based	57,259
Other real estate owned, including covered other real estate owned	$ 42,617
Bond pricing | Level 3 | Fair Value, Measurements, Recurring | Municipal Securities
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Bond pricing
Significant Unobservable Input	Equivalent rating
Range of Inputs	BBB-AA+
Impact to valuation from an increased or higher input value	Increase
Bond pricing | Level 3 | Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Bond pricing
Significant Unobservable Input	Equivalent rating
Range of Inputs	AAA
Impact to valuation from an increased or higher input value	Increase
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for- investment
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Discounted cash flows
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Discount Rate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Discount rate
Range of Inputs	3%-4%
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Discount Rate | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	3.70%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Discount Rate | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	3.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Discount Rate | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	4.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Credit Spread
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Credit loss rate
Range of Inputs	0%-3%
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Credit Spread | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit loss rate	0.89%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Credit Spread | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit loss rate	0.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Credit Spread | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Credit loss rate	3.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Constant Prepayment Rate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Constant prepayment rate (CPR)
Constant prepayment rate (CPR)	9.42%
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Loans held-for-investment Constant Prepayment Rate | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Constant prepayment rate (CPR)	9.42%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Discounted cash flows
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Discount Rate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Discount rate
Range of Inputs	9%-16%
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Discount Rate | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	9.81%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Discount Rate | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	9.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Discount Rate | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	16.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Prepayment Rate
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Constant prepayment rate (CPR)
Range of Inputs	0%-34%
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Prepayment Rate | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Constant prepayment rate (CPR)	9.64%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Prepayment Rate | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Constant prepayment rate (CPR)	0.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Prepayment Rate | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Constant prepayment rate (CPR)	34.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Cost of servicing
Range of Inputs	$65-$75
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing (in dollars per loan) | $ / Loan	65
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing (in dollars per loan) | $ / Loan	65
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing (in dollars per loan) | $ / Loan	75
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing - delinquent
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Significant Unobservable Input	Cost of servicing - delinquent
Range of Inputs	$200-$1,000
Impact to valuation from an increased or higher input value	Decrease
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing - delinquent | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing - delinquent (in dollars per loan) | $ / Loan	422
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing - delinquent | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing - delinquent (in dollars per loan) | $ / Loan	200
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Mortgage Servicing Rights Cost of servicing - delinquent | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Cost of servicing - delinquent (in dollars per loan) | $ / Loan	1,000
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Derivatives
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Discounted cash flows
Significant Unobservable Input	Pull-through rate
Range of Inputs	40%-100%
Impact to valuation from an increased or higher input value	Increase
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Derivatives | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull-through rate	89.79%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Derivatives | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull-through rate	40.00%
Discounted cash flows | Level 3 | Fair Value, Measurements, Recurring | Derivatives | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Pull-through rate	100.00%
Appraisal value | Level 3 | Fair Value, Measurements, Nonrecurring | Impaired loans—collateral based
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Appraisal value
Significant Unobservable Input	Appraisal adjustment - cost of sale
Range of Inputs	10%
Appraisal adjustment - cost of sale	10.00%
Impact to valuation from an increased or higher input value	Decrease
Appraisal value | Level 3 | Fair Value, Measurements, Nonrecurring | Impaired loans—collateral based | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraisal adjustment - cost of sale	10.00%
Appraisal value | Level 3 | Fair Value, Measurements, Nonrecurring | Other real estate owned, including covered other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Methodology	Appraisal value
Significant Unobservable Input	Appraisal adjustment - cost of sale
Range of Inputs	10%
Appraisal adjustment - cost of sale	10.00%
Impact to valuation from an increased or higher input value	Decrease
Appraisal value | Level 3 | Fair Value, Measurements, Nonrecurring | Other real estate owned, including covered other real estate owned | Weighted Average
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Appraisal adjustment - cost of sale	10.00%