Consolidated Statements of Changes in Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principles	$ 6,322			$ 6,322	$ 0
Adjusted balance	2,695,892	$ 175,141	$ 2,031,695	534,006	(44,950)
Beginning balance at Dec. 31, 2018	2,689,570	175,141	2,031,695	527,684	(44,950)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,276			56,276
Other comprehensive income (loss)	47,570				47,570
Dividends - common stock	(22,812)			(22,812)
Common stock issued	130	9	121
Common stock repurchased	(27,297)	(1,655)	(25,642)
Share-based compensation expense	1,800		1,800
Stock activity under incentive compensation plans	313	484	(12)	(159)
Ending balance at Mar. 31, 2019	2,751,872	173,979	2,007,962	567,311	2,620
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principles	(31,150)			(31,150)
Adjusted balance	2,821,303	169,616	1,944,445	651,035	56,207
Beginning balance at Dec. 31, 2019	2,852,453	169,616	1,944,445	682,185	56,207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,640			22,640
Other comprehensive income (loss)	81,950				81,950
Dividends - common stock	(23,535)			(23,535)
Common stock issued	151	9	142
Common stock repurchased	(81,822)	(5,076)	(76,746)
Share-based compensation expense	2,748		2,748
Stock activity under incentive compensation plans	0	560	(329)	(231)
Ending balance at Mar. 31, 2020	$ 2,823,435	$ 165,109	$ 1,870,260	$ 649,909	$ 138,157