Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions
Salaries and benefits	$ 108,684	$ 101,451	$ 96,513
Interest expense	17,661	18,060	18,606
Acquisition Expense	2,821	795	4,017
Earnings before income tax benefit	145,259	130,457	129,615
Income tax benefit	49,623	43,662	45,214
Net income	95,636	86,795	84,401
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	140,000	70,000	58,900
Other interest income	31	23	42
Other income, primarily management fees from subsidiaries	15,111	13,207	12,166
Total income	155,142	83,230	71,108
Salaries and benefits	18,757	16,267	15,722
Interest expense	4,173	3,844	4,002
Acquisition Expense	1,504	795	4,017
Other operating expenses, net	10,391	9,920	7,512
Total expenses	34,825	30,826	31,253
Earnings before income tax benefit	120,317	52,404	39,855
Income tax benefit	(7,670)	(6,952)	(6,862)
Income before undistributed earnings of subsidiaries	127,987	59,356	46,717
Undistributed earnings of subsidiaries	(32,351)	27,439	37,684
Net income	$ 95,636	$ 86,795	$ 84,401