Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Treasury Stock at Cost [Member]	Unearned Employee Stock Ownership Plan [Member]	Total
Balance at Dec. 31, 2011	$ 8,058	$ 1,078,743	$ 277,195	$ (7,938)	$ (53,640)	$ (313)	$ 1,302,105
Balance, Shares at Dec. 31, 2011	53,720
Net income			138,573				138,573
Unrealized gain on securities, net of tax				8,684			8,684
Unrealized loss on cash flow hedging activities, net of tax				3,045			3,045
Foreign currency translation adjustment, net of tax				1,127			1,127
Purchase of treasury stock					(11,380)		(11,380)
Employee stock ownership plan purchases		1,473				209	1,682
Issuance of stock for employee benefit plans, Shares	281
Issuance of stock for employee benefit plans	42	(59,357)	(31,798)		53,350		(37,763)
Stock option exercises, Shares	276
Stock option exercises	41	(9,718)			8,044		(1,633)
Unit amortization		51,207					51,207
Excess tax benefit from stock-based compensation		16,722					16,722
Issuance of common stock for acquisitions, Shares	691
Issuance of common stock for acquisitions	104	21,646					21,750
Warrant exercises, Shares		(579)			1,121		542
Balance at Dec. 31, 2012	8,245	1,100,137	383,970	4,918	(2,505)	(104)	1,494,661
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 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		715				104	819
Issuance of stock for employee benefit plans, Shares	1,774
Issuance of stock for employee benefit plans	266	(68,897)	(5,074)		13,913		(59,792)
Stock option exercises, Shares	28
Stock option exercises	5	(1,552)			2,198		651
Unit amortization		148,215					148,215
Excess tax benefit from stock-based compensation		12,018					12,018
Stone and Youngberg contingent earn-out, Shares	87
Stone and Youngberg contingent earn-out	13	3,253					3,266
Issuance of common stock for acquisitions, Shares	6,887
Issuance of common stock for acquisitions	1,033	264,033					265,066
Exchange of restricted awards - acquisitions		86,221					86,221
Warrant exercises			(671)				(671)
Balance at Dec. 31, 2013	9,562	1,544,143	540,238	(35,030)	(64)		2,058,849
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 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, Shares	2,158
Issuance of stock for employee benefit plans	324	(67,653)			64		(67,265)
Stock option exercises, Shares	33						34
Stock option exercises	4	312					316
Unit amortization		118,271					118,271
Excess tax benefit from stock-based compensation		19,858					19,858
Issuance of common stock for acquisitions, Shares	401
Issuance of common stock for acquisitions	60	19,183					19,243
Balance at Dec. 31, 2014	$ 9,950	$ 1,634,114	$ 716,305	$ (38,331)			$ 2,322,038
Balance, Shares at Dec. 31, 2014	66,336