Acquisitions Unaudited Pro Forma Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Business Acquisition, Pro Forma interest and dividend income	$ 313,851	$ 301,838
Business Acquisition, Pro Forma interest expense	21,750	26,386
Business Acquisition, Pro Forma net interest income	292,101	275,452
Business Acquisition, Pro Forma provision for loan losses	6,500	7,484
Business Acquisition, Pro Forma net interest income after provision for loan losses	285,601	267,968
Business Acquisition, Pro Forma noninterest income	83,447	86,243
Business Acquisition, Pro Forma noninterest expense	237,146	243,618
Business Acquisition, Pro Forma pre-tax net income	131,902	110,593
Business Acquisition, Pro Forma federal income tax expense	30,680	31,138
Business Acquisition, Pro Forma Net Income (Loss)	$ 101,222	$ 79,455
Business Acquisition, Pro Forma Earnings Per Share, Basic	$ 2.66	$ 2.17
Business Acquisition, Pro Forma Earnings Per Share, Diluted	$ 2.64	$ 2.16
Weighted Average Number of Shares Outstanding, Basic			28,183
Weighted Average Number of Shares Outstanding, Diluted	36,353	31,588	28,352