Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Impact of ASU No. 2016-13	As reported under ASU No. 2016-13	Common stock	Common stock As reported under ASU No. 2016-13	Retained earnings	Retained earnings Impact of ASU No. 2016-13	Retained earnings As reported under ASU No. 2016-13	Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) As reported under ASU No. 2016-13
Balance (in shares) at Dec. 31, 2017				108,788,000
Beginning Balance at Dec. 31, 2017	$ 2,097,386			$ 1,662,491		$ 476,836			$ (41,941)
Increase (decrease) in stockholders' equity
Net income for common stock	201,774					201,774
Other comprehensive income (loss), net of taxes (benefits)	(8,669)								(8,669)
Issuance of common stock:
Share-based plans (in shares)				91,000
Share-based plans	2,650			$ 2,650
Share-based expenses and other, net	4,126			4,126
Common stock dividends	(134,987)					(134,987)
Ending Balance at Dec. 31, 2018	2,162,280			$ 1,669,267		543,623			(50,610)
Balance (in shares) at Dec. 31, 2018				108,879,000
Increase (decrease) in stockholders' equity
Net income for common stock	217,882					217,882
Other comprehensive income (loss), net of taxes (benefits)	30,571								30,571
Issuance of common stock:
Share-based plans (in shares)				94,000
Share-based plans	3,092			$ 3,092
Share-based expenses and other, net	5,898			5,898
Common stock dividends	(139,463)					(139,463)
Ending Balance at Dec. 31, 2019	$ 2,280,260	$ (15,372)	$ 2,264,888	$ 1,678,257	$ 1,678,257	622,042	$ (15,372)	$ 606,670	(20,039)	$ (20,039)
Balance (in shares) at Dec. 31, 2019	108,973,328			108,973,000	108,973,000
Issuance of common stock:
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income for common stock	$ 197,824					197,824
Other comprehensive income (loss), net of taxes (benefits)	18,775								18,775
Share-based plans (in shares)				208,000
Share-based plans	3,973			$ 3,973
Share-based expenses and other, net	(3,862)			(3,862)
Common stock dividends	(144,096)					(144,096)
Ending Balance at Dec. 31, 2020	$ 2,337,502			$ 1,678,368		$ 660,398			$ (1,264)
Balance (in shares) at Dec. 31, 2020	109,181,124			109,181,000