Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		13,750	53,872,272
Beginning balance at Dec. 31, 2017	$ 3,696,791	$ 132,097	$ 53,872	$ 2,787,484	$ 769,226	$ (45,888)
Increase (Decrease) in Shareholders' Equity
Net income	240,210				240,210
Other comprehensive income (loss)	(87,476)					(87,476)
Cash dividends declared	(64,288)				(64,288)
Preferred stock dividends	(8,146)				(8,146)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			109,983
Common stock issued under incentive plans, net of shares surrendered in payment	(3,142)		$ 110	(3,252)
Common stock issued for acquisitions (in shares)			2,787,773
Common stock issued for acquisitions	214,659		$ 2,788	211,871
Common stock repurchases (in shares)			(763,210)
Common stock repurchases	(61,046)		$ (763)	(60,283)
Share-based compensation expense	15,144			15,144
Ending balance (in shares) at Sep. 30, 2018		13,750	56,006,818
Ending balance at Sep. 30, 2018	3,942,361	$ 132,097	$ 56,007	2,950,964	936,657	(133,364)
Beginning balance (in shares) at Jun. 30, 2018		13,750	56,390,387
Beginning balance at Jun. 30, 2018	3,913,409	$ 132,097	$ 56,390	2,976,833	860,073	(111,984)
Increase (Decrease) in Shareholders' Equity
Net income	101,465				101,465
Other comprehensive income (loss)	(21,380)					(21,380)
Cash dividends declared	(21,282)				(21,282)
Preferred stock dividends	(3,599)				(3,599)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			(20,359)
Common stock issued under incentive plans, net of shares surrendered in payment	(1,040)		$ (20)	(1,020)
Common stock repurchases (in shares)			(363,210)
Common stock repurchases	(30,376)		$ (363)	(30,013)
Share-based compensation expense	5,164			5,164
Ending balance (in shares) at Sep. 30, 2018		13,750	56,006,818
Ending balance at Sep. 30, 2018	3,942,361	$ 132,097	$ 56,007	2,950,964	936,657	(133,364)
Beginning balance (in shares) at Dec. 31, 2018		13,750	54,796,231
Beginning balance at Dec. 31, 2018	4,056,277	$ 132,097	$ 54,796	2,869,416	1,042,718	(42,750)
Increase (Decrease) in Shareholders' Equity
Net income	301,579				301,579
Other comprehensive income (loss)	96,693					96,693
Cash dividends declared	(69,720)				(69,720)
Preferred stock dividends	(8,146)				(8,146)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			169,656
Common stock issued under incentive plans, net of shares surrendered in payment	(4,178)		$ 170	(4,348)
Common stock issued for acquisitions (in shares)		10,000
Common stock issued for acquisitions	96,388	$ 96,388
Common stock repurchases (in shares)			(2,700,000)
Common stock repurchases	(204,740)		$ (2,700)	(202,040)
Share-based compensation expense	17,300			17,300
Ending balance (in shares) at Sep. 30, 2019		23,750	52,265,887
Ending balance at Sep. 30, 2019	4,283,300	$ 228,485	$ 52,266	2,680,328	1,268,278	53,943
Beginning balance (in shares) at Jun. 30, 2019		23,750	52,805,461
Beginning balance at Jun. 30, 2019	4,238,000	$ 228,485	$ 52,805	2,714,074	1,195,546	47,090
Increase (Decrease) in Shareholders' Equity
Net income	99,850				99,850
Other comprehensive income (loss)	6,853					6,853
Cash dividends declared	(23,519)				(23,519)
Preferred stock dividends	(3,599)				(3,599)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			12,656
Common stock issued under incentive plans, net of shares surrendered in payment	270		$ 13	257
Common stock repurchases (in shares)			(552,230)
Common stock repurchases	(40,016)		$ (552)	(39,464)
Share-based compensation expense	5,461			5,461
Ending balance (in shares) at Sep. 30, 2019		23,750	52,265,887
Ending balance at Sep. 30, 2019	$ 4,283,300	$ 228,485	$ 52,266	$ 2,680,328	$ 1,268,278	$ 53,943