CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Retained earnings	Accumulated other comprehensive income (loss)	Treasury stock	Cumulative Effect, Period of Adoption, Adjustment [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 2,078,249	$ 1,633,256	$ 600,014	$ (44,408)	$ (110,613)	$ 3,542	$ 2,636
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest | Accounting Standards Update 2016-01 [Member]				906
Beginning Balances (in shares) at Dec. 31, 2018		104,281,794			(6,387,508)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,542		98,542
Other comprehensive income (loss)	48,695			48,695
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(43,462)		(43,462)
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)					280,846
Restricted stock awards, net of forfeitures	(2,229)	(6,225)			$ 3,996
Share-based compensation expense	4,762	$ 4,762
Ending Balances (in shares) at Jun. 30, 2019		104,281,794			(5,634,104)
Ending Balances at Jun. 30, 2019	2,188,189		657,730	5,193	$ (98,433)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,130,419	$ 1,622,554	626,408	(19,635)	$ (98,908)	415	415
Beginning Balances (in shares) at Mar. 31, 2019		104,281,794			(5,667,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	52,703		52,703
Other comprehensive income (loss)	24,828			24,828
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(21,796)		(21,796)
Restricted stock awards, net of forfeitures (in shares)					33,818
Restricted stock awards, net of forfeitures	(146)	$ (621)			$ 475
Share-based compensation expense	1,766	$ 1,766
Ending Balances (in shares) at Jun. 30, 2019		104,281,794			(5,634,104)
Ending Balances at Jun. 30, 2019	2,188,189		657,730	5,193	$ (98,433)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 1,623,699	657,730	5,193
Retained Earnings (Accumulated Deficit)	711,249
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,247,705	$ 1,640,771	711,249	13,323	$ (117,638)	$ (56,882)	$ (56,882)
Beginning Balances (in shares) at Dec. 31, 2019		104,281,794			(5,790,796)
Beginning Balances at Dec. 31, 2019	2,247,705
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	66,021		66,021
Other comprehensive income (loss)	23,108			23,108
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(44,856)		(44,856)
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)					397,455
Restricted stock awards, net of forfeitures	(1,196)	(9,294)			$ 8,098
Share-based compensation expense	3,733	$ 3,733
Ending Balances (in shares) at Jun. 30, 2020		104,281,794			(6,262,936)
Ending Balances at Jun. 30, 2020	2,221,019	$ 1,635,070	675,532	36,431	$ (126,014)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,179,383	$ 1,633,950	660,653	11,788	$ (127,008)
Beginning Balances (in shares) at Mar. 31, 2020		104,281,794			(6,312,836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,393		37,393
Other comprehensive income (loss)	24,643			24,643
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(22,514)		(22,514)
Restricted stock awards, net of forfeitures (in shares)					49,900
Restricted stock awards, net of forfeitures	(82)	$ (1,076)			$ 994
Share-based compensation expense	2,196	$ 2,196
Ending Balances (in shares) at Jun. 30, 2020		104,281,794			(6,262,936)
Ending Balances at Jun. 30, 2020	2,221,019	$ 1,635,070	$ 675,532	$ 36,431	$ (126,014)
Retained Earnings (Accumulated Deficit)	$ 675,532