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, 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]
Net income	45,839		45,839
Other comprehensive income (loss)	23,867			23,867
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	3,127		2,221	906
Beginning Balances (in shares) at Dec. 31, 2019		104,281,794			(5,790,796)
Beginning Balances at Dec. 31, 2019	2,247,705	$ 1,640,771	711,249	13,323	$ (117,638)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,628		28,628
Other comprehensive income (loss)	(1,535)			(1,535)
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(22,342)		(22,342)
Treasury Stock, Shares, Acquired					(880,000)
Treasury Stock, Value, Acquired, Cost Method	(16,686)				$ (16,686)
Exercise of stock options, net of shares purchased (in shares)					10,405
Exercise of stock options, net of shares purchased	(72)	(140)			$ (212)
Restricted stock awards, net of forfeitures (in shares)					347,555
Restricted stock awards, net of forfeitures	(1,114)	(8,218)			$ 7,104
Share-based compensation expense	1,537	$ 1,537
Ending Balances (in shares) at Mar. 31, 2020		104,281,794			(6,312,836)
Ending Balances at Mar. 31, 2020	2,179,383	$ 1,633,950	660,653	$ 11,788	$ (127,008)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (56,882)		$ (56,882)