CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Retained earnings	Accumulated other comprehensive income (loss)	Treasury stock
Beginning Balances (in shares) at Dec. 31, 2016		68,730,731			(6,751,179)
Beginning Balances at Dec. 31, 2016	$ 865,224	$ 570,382	$ 437,188	$ (28,443)	$ (113,903)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	71,976		71,976
Other comprehensive income (loss)	8,064			8,064
Cash dividends declared :
Common stock at $0.58 per share in 2018 and $0.51 per share in 2017	(31,576)		(31,576)
Stock Issued During Period, Shares, Other					4,848
Adjustments to Additional Paid in Capital, Other	0	(82)			$ 82
Exercise of stock options, net of shares purchased (in shares)					53,303
Exercise of stock options, net of shares purchased	18	(885)			$ 903
Restricted stock awards, net of forfeitures (in shares)					23,762
Restricted stock awards, net of forfeitures	(2,783)	(1,696)			$ (1,087)
Share-based compensation expense	4,031	$ 4,031
Ending Balances (in shares) at Sep. 30, 2017		68,730,731			(6,669,266)
Ending Balances at Sep. 30, 2017	914,954	$ 571,750	477,588	(20,379)	$ (114,005)
Beginning Balances (in shares) at Dec. 31, 2017		68,730,731			(6,661,644)
Beginning Balances at Dec. 31, 2017	930,664	$ 573,109	491,847	(20,390)	$ (113,902)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	0		5,092	(5,092)
Net income	117,581		117,581
Other comprehensive income (loss)	(27,415)			(27,415)
Cash dividends declared :
Common stock at $0.58 per share in 2018 and $0.51 per share in 2017	(49,975)		(49,975)
Stock Issued During Period, Shares, New Issues		35,551,063
Stock Issued During Period, Value, Acquisitions	1,045,876	$ 1,045,876
Stock Options and Warrants Acquired And Converted Pursuant To Acquisition	16,037	16,037
Stock Issued During Period, Shares, Other					57,530
Adjustments to Additional Paid in Capital, Other	0	(984)			$ 984
Exercise of stock options, net of shares purchased (in shares)					32,941
Exercise of stock options, net of shares purchased	284	(282)			$ 566
Restricted stock awards, net of forfeitures (in shares)					203,905
Restricted stock awards, net of forfeitures	(2,517)	(4,913)			$ 2,396
Share-based compensation expense	4,985	$ 4,985
Ending Balances (in shares) at Sep. 30, 2018		104,281,794			(6,367,268)
Ending Balances at Sep. 30, 2018	$ 2,035,520	$ 1,633,828	$ 564,545	$ (52,897)	$ (109,956)