Consolidated Statements Of Changes In Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Treasury Stock at Cost [Member]	Unearned Employee Stock Ownership Plan [Member]
Balance at Dec. 31, 2012	$ 1,494,661	$ 8,245	$ 1,100,137	$ 383,970	$ 4,918	$ (2,505)	$ (104)
Balance, Shares at Dec. 31, 2012		54,968
Net income	162,013			162,013
Unrealized gain on securities, net of tax	(48,528)				(48,528)
Unrealized gain (loss) on cash flow hedging activities, net of tax	6,917				6,917
Foreign currency translation adjustment, net of tax	1,663				1,663
Purchase of treasury stock	(13,670)					(13,670)
Employee stock ownership plan purchases	819		715				$ 104
Issuance of stock for employee benefit plans	(59,792)	$ 266	(68,897)	(5,074)		13,913
Issuance of stock for employee benefit plans, Shares		1,774
Stock option exercises	651	$ 5	(1,552)			2,198
Stock option exercises, Shares		28
Unit amortization	148,215		148,215
Excess tax benefit from stock-based compensation	12,018		12,018
Issuance of common stock for acquisitions	265,066	$ 1,033	264,033
Stock Issued During Period Shares Acquisitions		6,887
Issuance of restricted stock awards for acquisitions	86,221		86,221
Stone & Youngberg contingent earn-out	3,266	$ 13	3,253
Stone and Youngberg contingent earn-out, Shares		87
Other	(671)			(671)
Balance at Dec. 31, 2013	2,058,849	$ 9,562	1,544,143	540,238	(35,030)	(64)
Balance, Shares at Dec. 31, 2013		63,744
Net income	176,067			176,067
Unrealized gain on securities, net of tax	1,838				1,838
Unrealized gain (loss) on cash flow hedging activities, net of tax	2,141				2,141
Foreign currency translation adjustment, net of tax	(7,280)				(7,280)
Issuance of stock for employee benefit plans	(67,265)	$ 324	(67,653)			64
Issuance of stock for employee benefit plans, Shares		2,158
Stock option exercises	316	$ 4	312
Stock option exercises, Shares		33
Unit amortization	118,271		118,271
Excess tax benefit from stock-based compensation	19,858		19,858
Issuance of common stock for acquisitions	19,243	$ 60	19,183
Stock Issued During Period Shares Acquisitions		401
Balance at Dec. 31, 2014	2,322,038	$ 9,950	1,634,114	716,305	(38,331)
Balance, Shares at Dec. 31, 2014		66,336
Net income	92,336			92,336
Unrealized gain on securities, net of tax	1,389				1,389
Unrealized gain (loss) on cash flow hedging activities, net of tax	1,088				1,088
Foreign currency translation adjustment, net of tax	(3,679)				(3,679)
Purchase of treasury stock	(117,752)					(117,752)
Issuance of stock for employee benefit plans	(66,000)	$ 263	(75,126)	(2,956)		11,819
Issuance of stock for employee benefit plans, Shares		1,754
Stock option exercises	$ 660	$ 3	(342)			999
Stock option exercises, Shares	44	17
Unit amortization	$ 167,848		167,848
Excess tax benefit from stock-based compensation	14,741		14,741
Issuance of common stock for acquisitions	79,747	$ 210	79,537
Stock Issued During Period Shares Acquisitions		1,400
Balance at Dec. 31, 2015	$ 2,492,416	$ 10,426	$ 1,820,772	$ 805,685	$ (39,533)	$ (104,934)
Balance, Shares at Dec. 31, 2015		69,507