Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Stock options	Common stock	Common stock Stock options	Additional paid-in capital	Additional paid-in capital Stock options	Retained earnings	Accumulated other comprehensive income (loss)
Changes in Stockholders' Equity
Cumulative effect adjustment of change in accounting policy, net of tax impact	[1]	$ 1,339						$ 1,680	$ (341)
Beginning balance at Dec. 31, 2017		2,668,749		$ 71,207		$ 2,203,637		419,403	(25,498)
Changes in Stockholders' Equity
Comprehensive income		119,072						140,584	(21,512)
Cash dividends		(40,137)						40,137
Net shares issued under share-based compensation plans			$ (2,102)		$ 211		$ (2,313)
Share-based compensation expense		4,078		0		4,078
Ending balance at Jun. 30, 2018		2,750,999		71,418		2,205,402		521,530	(47,351)
Beginning balance at Mar. 31, 2018		2,704,703		71,350		2,201,803		472,604	(41,054)
Changes in Stockholders' Equity
Comprehensive income		62,691						68,988	(6,297)
Cash dividends		(20,062)						(20,062)
Net shares issued under share-based compensation plans			1,241		68		1,173
Share-based compensation expense		2,426		0		2,426
Ending balance at Jun. 30, 2018		2,750,999		71,418		2,205,402		521,530	(47,351)
Beginning balance at Dec. 31, 2018		2,836,260		71,460		2,209,761		616,149	(61,110)
Changes in Stockholders' Equity
Comprehensive income		163,245						132,536	30,709
Cash dividends		(48,973)						(48,973)
Net shares issued under share-based compensation plans			(2,126)		99		(2,225)
Share-based compensation expense		5,129		0		5,129
Ending balance at Jun. 30, 2019		2,953,535		71,559		2,212,665		699,712	(30,401)
Beginning balance at Mar. 31, 2019		2,897,509		71,551		2,209,860		654,605	(38,507)
Changes in Stockholders' Equity
Comprehensive income		77,700						69,594	8,106
Cash dividends		(24,487)						(24,487)
Net shares issued under share-based compensation plans			$ 57		$ 8		$ 49
Share-based compensation expense		2,756		0		2,756
Ending balance at Jun. 30, 2019		$ 2,953,535		$ 71,559		$ 2,212,665		$ 699,712	$ (30,401)

[1] Refer to Note 1, Basis of Presentation and Significant Accounting Policies, Note 6, Other Real Estate Owned and Repossessed Assets and Note 20, Accumulated Other Comprehensive Loss for further details on the changes in accounting policy.