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, 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		5,093	(5,093)
Net income	30,506		30,506
Other comprehensive income (loss)	(9,351)			(9,351)
Cash dividends declared :
Common stock at $0.22 per share in 2019 and $0.19 per share in 2018	(11,797)		(11,797)
Stock Issued During Period, Shares, Other					1,428
Adjustments to Additional Paid in Capital, Other	0	(24)			$ 24
Exercise of stock options, net of shares purchased (in shares)					11,800
Exercise of stock options, net of shares purchased	137	(65)			$ 202
Restricted stock awards, net of forfeitures (in shares)					131,508
Restricted stock awards, net of forfeitures	(2,128)	(3,517)			$ 1,389
Share-based compensation expense	1,954	$ 1,954
Ending Balances (in shares) at Mar. 31, 2018		68,730,731			(6,516,908)
Ending Balances at Mar. 31, 2018	939,985	$ 571,457	515,649	(34,834)	$ (112,287)
Beginning Balances (in shares) at Dec. 31, 2018		104,281,794			(6,387,508)
Beginning Balances at Dec. 31, 2018	2,078,249	$ 1,633,256	600,014	(44,408)	$ (110,613)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	3,127		2,221	906
Net income	45,839		45,839
Other comprehensive income (loss)	23,867			23,867
Cash dividends declared :
Common stock at $0.22 per share in 2019 and $0.19 per share in 2018	(21,666)		(21,666)
Stock Issued During Period, Shares, Other					452,134
Adjustments to Additional Paid in Capital, Other	0	(7,830)			$ 7,830
Exercise of stock options, net of shares purchased (in shares)					20,424
Exercise of stock options, net of shares purchased	90	(264)			$ 354
Restricted stock awards, net of forfeitures (in shares)					247,028
Restricted stock awards, net of forfeitures	(2,083)	(5,604)			$ 3,521
Share-based compensation expense	2,996	$ 2,996
Ending Balances (in shares) at Mar. 31, 2019		104,281,794			(5,667,922)
Ending Balances at Mar. 31, 2019	$ 2,130,419	$ 1,622,554	$ 626,408	$ (19,635)	$ (98,908)