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	149,398		149,398
Other comprehensive income (loss)	58,952			58,952
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(66,680)		(66,680)
Treasury Stock, Shares, Acquired					(1,143,494)
Treasury Stock, Value, Acquired, Cost Method	(27,372)				$ (27,372)
Stock Issued During Period, Shares, Acquisitions					2,601,823
Stock Issued During Period, Value, Acquisitions	60,934	$ 13,658			$ 47,276
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)					269,646
Restricted stock awards, net of forfeitures	(2,267)	(5,954)			$ 3,687
Share-based compensation expense	6,467	$ 6,467
Ending Balances (in shares) at Sep. 30, 2019		104,281,794			(4,186,975)
Ending Balances at Sep. 30, 2019	2,261,313		685,368	15,450	$ (78,838)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,188,189	$ 1,623,699	657,730	5,193	$ (98,433)
Beginning Balances (in shares) at Jun. 30, 2019		104,281,794			(5,634,104)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,856		50,856
Other comprehensive income (loss)	10,257			10,257
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(23,218)		(23,218)
Treasury Stock, Shares, Acquired					(1,143,494)
Treasury Stock, Value, Acquired, Cost Method	(27,372)				$ (27,372)
Stock Issued During Period, Shares, Acquisitions					2,601,823
Stock Issued During Period, Value, Acquisitions	60,934	$ 13,658			$ 47,276
Restricted stock awards, net of forfeitures (in shares)					(11,200)
Restricted stock awards, net of forfeitures	(38)	271			$ (309)
Share-based compensation expense	1,705	$ 1,705
Ending Balances (in shares) at Sep. 30, 2019		104,281,794			(4,186,975)
Ending Balances at Sep. 30, 2019	2,261,313		685,368	15,450	$ (78,838)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 1,639,333	685,368	15,450
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	107,498		107,498
Other comprehensive income (loss)	28,943			28,943
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(67,381)		(67,381)
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)					378,360
Restricted stock awards, net of forfeitures	(1,203)	(8,891)			$ 7,688
Share-based compensation expense	5,749	$ 5,749
Ending Balances (in shares) at Sep. 30, 2020		104,281,794			(6,282,031)
Ending Balances at Sep. 30, 2020	2,247,815	$ 1,637,489	694,484	42,266	$ (126,424)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,221,019	$ 1,635,070	675,532	36,431	$ (126,014)
Beginning Balances (in shares) at Jun. 30, 2020		104,281,794			(6,262,936)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41,477		41,477
Other comprehensive income (loss)	5,835			5,835
Cash dividends declared :
Common stock at $0.23 per share in 2020 and $0.22 per share in 2019	(22,525)		(22,525)
Restricted stock awards, net of forfeitures (in shares)					(19,095)
Restricted stock awards, net of forfeitures	(7)	$ 403			$ (410)
Share-based compensation expense	2,016	$ 2,016
Ending Balances (in shares) at Sep. 30, 2020		104,281,794			(6,282,031)
Ending Balances at Sep. 30, 2020	2,247,815	$ 1,637,489	$ 694,484	$ 42,266	$ (126,424)
Retained Earnings (Accumulated Deficit)	$ 694,484