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		155,283						140,077	15,206
Cash dividends		(58,504)						(58,504)
Net shares issued under share-based compensation plans			$ (23,448)		$ 553		$ (24,001)
Share-based compensation expense		14,573		0		14,573
Ending balance at Sep. 30, 2017		2,673,089		71,152		2,201,334		425,433	(24,830)
Beginning balance at Jun. 30, 2017		2,639,442		71,131		2,197,501		404,939	(34,129)
Changes in Stockholders' Equity
Comprehensive income		49,758						40,459	9,299
Cash dividends		(19,965)						(19,965)
Net shares issued under share-based compensation plans			(3,792)		21		(3,813)
Share-based compensation expense		7,646		0		7,646
Ending balance at Sep. 30, 2017		2,673,089		71,152		2,201,334		425,433	(24,830)
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		179,165						210,981	(31,816)
Cash dividends		(64,554)						(64,554)
Net shares issued under share-based compensation plans			(1,766)		231		(1,997)
Share-based compensation expense		5,991		0		5,991
Ending balance at Sep. 30, 2018		2,788,924		71,438		2,207,631		567,510	(57,655)
Beginning balance at Jun. 30, 2018		2,750,999		71,418		2,205,402		521,530	(47,351)
Changes in Stockholders' Equity
Comprehensive income		60,093						70,397	(10,304)
Cash dividends		(24,417)						(24,417)
Net shares issued under share-based compensation plans			$ 336		$ 20		$ 316
Share-based compensation expense		1,913		0		1,913
Ending balance at Sep. 30, 2018		$ 2,788,924		$ 71,438		$ 2,207,631		$ 567,510	$ (57,655)

[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.