Benefit Plans - Additional Information (Detail) - USD ($)			12 Months Ended
	Jan. 01, 2018	Jan. 29, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net actuarial loss expected to be recognized as a component of net periodic pension expense			$ 309,000
Discount rate used to compute the obligation			4.30%	3.69%
Projected benefit obligation			$ 157,364,000	$ 170,566,000
Salary expense			18,800,000	10,800,000	$ 10,500,000
Expense for contributions to savings and investment plan			$ 8,500,000	7,100,000	6,700,000
Shares of common stock were available for issuance (in shares)			5,500,000
Stock-based compensation expense			$ 19,472,000	$ 12,204,000	$ 10,032,000
Unrecognized stock-based compensation			$ 16,600,000
Average remaining vesting, years			2 years 1 month 6 days
Shares outstanding in connection with acquisition (in shares)			1,051,787	446,980	732,489		1,383,365
Director Restricted Stock Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Additional fees		$ 0
Stock Options and Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation expense			$ 19,500,000	$ 12,200,000	$ 10,000,000
Stock awards granted			$ 4,300,000	$ 4,300,000	$ 3,500,000
Stock Options and Restricted Stock | Employee Stock Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Weighted average grant date fair value (usd per share)			$ 12.36	$ 11.05	$ 8.32
RSUs
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)			509,725	370,681	431,069
Vested (in shares)			503,879	0	0
Performance Shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			3 years
Stock-based compensation			$ 5,500,000	$ 3,800,000	$ 2,800,000
Performance Shares | Employee Stock Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Weighted average grant date fair value (usd per share)			$ 11.85
Performance Shares | Vesting based on growth in tangible book value per share plus dividends | Employee Stock Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Annual vesting percentage			75.00%
Performance Shares | Vesting based on total shareholder return as compared to our peer group | Employee Stock Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Annual vesting percentage			25.00%
Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)			1,263,144	608,786	544,307
Vested (in shares)			1,128,521	736,575	1,050,293
Performance Based Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)						240,000
Vested (in shares)				85,000	53,000
Minimum | Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			1 year
Maximum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			10 years
Maximum | Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			5 years
Non-Employee Directors | RSUs
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)			60,000	45,000
Grant date fair value of awards			$ 60,000	$ 50,000
Qualified Plan | Equity securities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation percentage			50.00%
Cumulative annual real return			7.00%
Qualified Plan | Equity securities | Consumer Price Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period			5 years
Qualified Plan | Equity securities | S&P 500 Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period			3 years
Qualified Plan | Fixed income securities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation percentage			50.00%
Cumulative annual real return			3.00%
Qualified Plan | Fixed income securities | Consumer Price Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period			5 years
Qualified Plan | Fixed income securities | Merrill Lynch Intermediate Government/Corporate Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period			3 years
Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation			$ 18,708,000	20,175,000
Nonqualified Plan | Former Directors And Senior Management
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation			512,000	682,000
Obligation included in other comprehensive loss, net of tax			872,000	994,000
Obligation included in other comprehensive loss, tax			345,000	$ 400,000
Obligation included in other comprehensive loss, net of tax, amount expected to be reclassified			$ 816,000
USAmeriBancorp, Inc.
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Shares in connection with acquisition (in shares)	1,800,000		1,803,165	0	0
Shares outstanding in connection with acquisition (in shares)			813,000
Weighted average exercise price in connection with acquisition	$ 5.47		$ 5	$ 0	$ 0
USAmeriBancorp, Inc. | RSUs
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Time-based RSUs in connection with acquisition			336,379	0	0
USAmeriBancorp, Inc. | Time Based Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Time-based RSUs in connection with acquisition	336,000
Time-based RSUs outstanding in connection with acquisition			179,000
Stock-based compensation			$ 1,600,000
Other pension plan | Nonqualified Plan | Non Qualified Plans For Former Directors
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation			$ 1,700,000	$ 2,100,000