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		49,675						47,604	2,071
Cash dividends declared and paid, $0.82 and $0.79 per share at September 30, 2017 and 2016, respectively		(19,271)						(19,271)
Net shares issued under share-based compensation plans			$ (19,272)		$ 518		$ (19,790)
Share-based compensation expense		3,734		1		3,733
Ending balance at Mar. 31, 2017		2,600,051		71,118		2,194,705		372,193	(37,965)
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		54,955						70,170	(15,215)
Cash dividends declared and paid, $0.82 and $0.79 per share at September 30, 2017 and 2016, respectively		(20,075)						(20,075)
Net shares issued under share-based compensation plans			$ (3,343)		$ 143		$ (3,486)
Share-based compensation expense		1,652		0		1,652
Ending balance at Mar. 31, 2018		$ 2,703,277		$ 71,350		$ 2,201,803		$ 471,178	$ (41,054)

[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.