Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Employee Stock Ownership Plan	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Common Stock Acquired by Deferred Compensation Plan	Deferred Compensation Plan Liability
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adopting Accounting Standards Update (ASU) | Accounting Standards Update 2016-09	$ 0			$ (11,129)	$ 11,129
Beginning Balance at Dec. 31, 2016	571,903	$ (2,761)	$ 336	364,433	238,192	$ (5,749)	$ (22,548)	$ (313)	$ 313
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,514				32,514
Other comprehensive income, net of tax	600					600
Stock awards	1,678			1,678
Treasury stock allocated to restricted stock plan	0			(1,645)	782		863
Allocation of ESOP stock	692	212		480
Cash dividend	(14,439)				(14,439)
Exercise of stock options	3,192				(2,125)		5,317
Sale (purchase) of stock for the deferred compensation plan								230	(230)
Ending Balance at Sep. 30, 2017	596,140	(2,549)	336	353,817	266,053	(5,149)	(16,368)	(83)	83
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of adopting Accounting Standards Update (ASU) | Accounting Standards Update 2016-01	0			0	(147)	147
Beginning Balance at Dec. 31, 2017	601,941	(2,479)	$ 336	354,377	271,023	(5,349)	(15,967)	(84)	84
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,200				45,200
Other comprehensive income, net of tax	1,259					1,259
Stock awards	2,530			2,528
Acquisition of common stock by ESOP	(8,400)	(8,400)
Allocation of ESOP stock	1,249	767		482
Cash dividend	(21,425)				(21,425)
Exercise of stock options (in shares)			4
Exercise of stock options	4,936			12,919	(8,189)		202
Acquisition of Sun Bancorp Inc. (shares)			141
Acquisition of Sun Bancorp Inc.	402,554			386,648			15,765
Sale (purchase) of stock for the deferred compensation plan								(3)	3
Ending Balance at Sep. 30, 2018	$ 1,029,844	$ (10,112)	$ 483	$ 756,954	$ 286,462	$ (3,943)	$ 0	$ (87)	$ 87