Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions
Salaries and benefits	$ 101,451	$ 96,513	$ 94,002
Interest expense	18,060	18,606	20,695
Acquisition Expense	795	4,017	0
Earnings before income tax benefit	130,457	129,615	132,702
Income tax benefit	43,662	45,214	46,566
Net income	86,795	84,401	86,136
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	70,000	58,900	71,400
Other interest income	23	42	34
Other income, primarily management fees from subsidiaries	13,207	12,166	12,809
Total income	83,230	71,108	84,243
Salaries and benefits	16,267	15,722	15,914
Interest expense	3,844	4,002	4,098
Acquisition Expense	795	4,017
Other operating expenses, net	9,920	7,512	7,546
Total expenses	30,826	31,253	27,558
Earnings before income tax benefit	52,404	39,855	56,685
Income tax benefit	(6,952)	(6,862)	(5,703)
Income before undistributed earnings of subsidiaries	59,356	46,717	62,388
Undistributed earnings of subsidiaries	27,439	37,684	23,748
Net income	$ 86,795	$ 84,401	$ 86,136