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]	$ 3,659						$ 3,659
Beginning balance at Dec. 31, 2016		2,581,526		$ 70,599		$ 2,210,762		340,201	$ (40,036)
Changes in Stockholders' Equity
Comprehensive income		105,525						99,618	5,907
Cash dividends		(38,539)						(38,539)
Net shares issued under share-based compensation plans			$ (19,657)		$ 531		$ (20,188)
Share-based compensation expense		6,928		1		6,927
Ending balance at Jun. 30, 2017		2,639,442		71,131		2,197,501		404,939	(34,129)
Beginning balance at Mar. 31, 2017									(37,965)
Changes in Stockholders' Equity
Comprehensive income		55,850
Ending balance at Jun. 30, 2017		2,639,442		71,131		2,197,501		404,939	(34,129)
Changes in Stockholders' Equity
Cumulative effect adjustment of change in accounting policy, net of tax impact	[2]	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									(41,054)
Changes in Stockholders' Equity
Comprehensive income		62,691
Ending balance at Jun. 30, 2018		$ 2,750,999		$ 71,418		$ 2,205,402		$ 521,530	$ (47,351)

[1] Refer to Note 1, Basis of Presentation and Significant Accounting Policies and Note 7, Loan Servicing Rights for further details on the changes in accounting policy.

[2] Refer to Note 1, Basis of Presentation and Significant Accounting Policies, Note 3, Investment Securities, Note 5, Other Real Estate Owned and Repossessed Assets and Note 9, Derivative Instruments and Balance Sheet Offsetting, for further details on the changes in accounting policy.