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	12,018				12,018
Other comprehensive income, net of tax	230					230
Stock awards	730			730
Treasury stock allocated to restricted stock plan	0			(1,892)	892		1,000
Allocation of ESOP stock	245	71		174
Cash dividend	(4,787)				(4,787)
Exercise of stock options	2,204			3,456	(1,399)		3,603
Acquisition of Sun Bancorp Inc.				386,648
Sale of stock for the deferred compensation plan								(3)	3
Ending Balance at Mar. 31, 2017	582,543	(2,690)	336	352,316	256,045	(5,519)	(17,945)	(316)	316
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	5,427				5,427
Other comprehensive income, net of tax	(104)					(104)
Stock awards	808			806
Allocation of ESOP stock	483	290		193
Cash dividend	(7,105)				(7,105)
Exercise of stock options (in shares)			2
Exercise of stock options	3,456				(204)		202
Acquisition of Sun Bancorp Inc. (shares)			141
Acquisition of Sun Bancorp Inc.	402,554						15,765
Ending Balance at Mar. 31, 2018	$ 1,007,460	$ (2,189)	$ 481	$ 745,480	$ 268,994	$ (5,306)	$ 0	$ (84)	$ 84