Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Stock options	Restricted stock units	Restricted stock awards	Common stock	Common stock Stock options	Common stock Restricted stock units	Common stock Restricted stock awards	Additional paid-in capital	Additional paid-in capital Stock options	Additional paid-in capital Restricted stock units	Additional paid-in capital Restricted stock awards	Retained earnings	Accumulated other comprehensive income (loss)
Beginning balance at Dec. 31, 2015		$ 1,015,974				$ 38,168				$ 725,280				$ 281,558	$ (29,032)
Changes in Stockholders' Equity
Comprehensive income		25,947												23,605	2,342
Cash dividends declared and paid, $0.27 and $0.26 per share at March 31, 2017 and March 31, 2016, respectively		(9,961)												(9,961)
Shares issued under share-based compensation			$ 309	$ (727)			$ 36	$ 43			$ 273	$ (770)
Share-based compensation expense		749				1				748
Ending balance at Mar. 31, 2016		1,032,291				38,248				725,531				295,202	(26,690)
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, $0.27 and $0.26 per share at March 31, 2017 and March 31, 2016, respectively		(19,271)												(19,271)
Shares issued under share-based compensation			$ (16,696)	$ (1,295)	$ (1,281)		$ 508	$ 35	$ (25)		$ (17,204)	$ (1,330)	$ (1,256)
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)

[1] Refer to Footnote 1, Basis of Presentation and Accounting Policies and Footnote 8, Loan Servicing Rights, for further details on this change in accounting policy election.