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	138,745				138,745
Other comprehensive income (loss)	(66,096)					(66,096)
Cash dividends declared	(43,006)				(43,006)
Preferred stock dividends	(4,547)				(4,547)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			130,342
Common stock issued under incentive plans, net of shares surrendered in payment	(2,102)		$ 130	(2,232)
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)			(400,000)
Common stock repurchases	(30,670)		$ (400)	(30,270)
Share-based compensation expense	9,980			9,980
Ending balance (in shares) at Jun. 30, 2018		13,750	56,390,387
Ending balance at Jun. 30, 2018	3,913,409	$ 132,097	$ 56,390	2,976,833	860,073	(111,984)
Beginning balance (in shares) at Mar. 31, 2018		13,750	56,778,841
Beginning balance at Mar. 31, 2018	3,900,907	$ 132,097	$ 56,779	3,001,389	807,325	(96,683)
Increase (Decrease) in Shareholders' Equity
Net income	75,124				75,124
Other comprehensive income (loss)	(15,301)					(15,301)
Cash dividends declared	(21,427)				(21,427)
Preferred stock dividends	(949)				(949)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			11,546
Common stock issued under incentive plans, net of shares surrendered in payment	479		$ 11	468
Common stock repurchases (in shares)			(400,000)
Common stock repurchases	(30,670)		$ (400)	(30,270)
Share-based compensation expense	5,246			5,246
Ending balance (in shares) at Jun. 30, 2018		13,750	56,390,387
Ending balance at Jun. 30, 2018	3,913,409	$ 132,097	$ 56,390	2,976,833	860,073	(111,984)
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	201,729				201,729
Other comprehensive income (loss)	89,840					89,840
Cash dividends declared	(46,201)				(46,201)
Preferred stock dividends	(4,547)				(4,547)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			157,000
Common stock issued under incentive plans, net of shares surrendered in payment	(4,448)		$ 157	(4,605)
Common stock issued for acquisitions (in shares)		10,000
Common stock issued for acquisitions	96,388	$ 96,388
Common stock repurchases (in shares)			(2,147,770)
Common stock repurchases	(164,724)		$ (2,148)	(162,576)
Share-based compensation expense	11,839			11,839
Ending balance (in shares) at Jun. 30, 2019		23,750	52,805,461
Ending balance at Jun. 30, 2019	4,238,000	$ 228,485	$ 52,805	2,714,074	1,195,546	47,090
Beginning balance (in shares) at Mar. 31, 2019		13,750	54,551,264
Beginning balance at Mar. 31, 2019	4,141,831	$ 132,097	$ 54,551	2,840,842	1,117,641	(3,300)
Increase (Decrease) in Shareholders' Equity
Net income	101,598				101,598
Other comprehensive income (loss)	50,390					50,390
Cash dividends declared	(22,744)				(22,744)
Preferred stock dividends	(949)				(949)
Common stock issued under incentive plans, net of shares surrendered in payment (in shares)			14,046
Common stock issued under incentive plans, net of shares surrendered in payment	(3)		$ 14	(17)
Common stock issued for acquisitions (in shares)		10,000
Common stock issued for acquisitions	96,388	$ 96,388
Common stock repurchases (in shares)			(1,759,849)
Common stock repurchases	(134,778)		$ (1,760)	(133,018)
Share-based compensation expense	6,267			6,267
Ending balance (in shares) at Jun. 30, 2019		23,750	52,805,461
Ending balance at Jun. 30, 2019	$ 4,238,000	$ 228,485	$ 52,805	$ 2,714,074	$ 1,195,546	$ 47,090