Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common stock	Retained earnings	Accumulated other comprehensive income (loss)
Beginning Balance at Dec. 31, 2016	$ 2,066,753	$ 1,660,910	$ 438,972	$ (33,129)
Balance (in shares) at Dec. 31, 2016		108,583,000
Increase (decrease) in stockholders' equity
Net income for common stock	165,297		165,297
Other comprehensive income (loss), net of tax benefits	(1,372)			(1,372)
Reclass of AOCI for tax rate reduction impact			7,440	(7,440)
Issuance of common stock: Share-based plans	4,664	$ 4,664
Issuance of common stock: Share-based plans (in shares)		205,000
Issuance of common stock: Share-based expenses and other, net	(3,083)	$ (3,083)
Common stock dividends	(134,873)		(134,873)
Ending Balance at Dec. 31, 2017	2,097,386	$ 1,662,491	476,836	(41,941)
Balance (in shares) at Dec. 31, 2017		108,788,000
Increase (decrease) in stockholders' equity
Net income for common stock	201,774		201,774
Other comprehensive income (loss), net of tax benefits	(8,669)			(8,669)
Issuance of common stock: Share-based plans	2,650	$ 2,650
Issuance of common stock: Share-based plans (in shares)		91,000
Issuance of common stock: 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	108,879,245	108,879,000
Increase (decrease) in stockholders' equity
Net income for common stock	$ 217,882		217,882
Other comprehensive income (loss), net of tax benefits	30,571			30,571
Issuance of common stock: Share-based plans	3,092	$ 3,092
Issuance of common stock: Share-based plans (in shares)		94,000
Issuance of common stock: 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	$ 1,678,257	$ 622,042	$ (20,039)
Balance (in shares) at Dec. 31, 2019	108,973,328	108,973,000