Investment Securities - Gross Unrealized Losses (Details) $ in Thousands	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($)
Schedule of Investments [Line Items]
Total number of securities, available-for-sale and held-to-maturity | security	2,309
Securities in unrealized loss positions, qualitative disclosure, number of positions | security	1,418
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	$ 1,463,173	$ 1,478,240
Less Than 12 Months, Gross Unrealized Losses	30,370	39,116
12 Months or More, Fair Value	51,664	56,897
12 Months or More, Gross Unrealized Losses	1,443	1,751
Total, Fair Value	1,514,837	1,535,137
Total, Gross Unrealized Losses	31,813	40,867
Government sponsored agencies
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	108,300	105,702
Less Than 12 Months, Gross Unrealized Losses	1,445	1,707
12 Months or More, Fair Value	11,203	15,023
12 Months or More, Gross Unrealized Losses	362	361
Total, Fair Value	119,503	120,725
Total, Gross Unrealized Losses	1,807	2,068
State and political subdivisions
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	705,870	758,063
Less Than 12 Months, Gross Unrealized Losses	19,603	28,158
12 Months or More, Fair Value	26,084	26,810
12 Months or More, Gross Unrealized Losses	718	975
Total, Fair Value	731,954	784,873
Total, Gross Unrealized Losses	20,321	29,133
Residential mortgage-backed securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	248,111	244,239
Less Than 12 Months, Gross Unrealized Losses	4,204	3,992
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	248,111	244,239
Total, Gross Unrealized Losses	4,204	3,992
Collateralized mortgage obligations
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	311,566	279,001
Less Than 12 Months, Gross Unrealized Losses	3,626	3,778
12 Months or More, Fair Value	12,528	14,754
12 Months or More, Gross Unrealized Losses	212	225
Total, Fair Value	324,094	293,755
Total, Gross Unrealized Losses	3,838	4,003
Corporate bonds
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	78,815	80,536
Less Than 12 Months, Gross Unrealized Losses	1,211	1,401
12 Months or More, Fair Value	1,499	0
12 Months or More, Gross Unrealized Losses	1	0
Total, Fair Value	80,314	80,536
Total, Gross Unrealized Losses	1,212	1,401
Trust preferred securities
Summary of continuous unrealized loss position of securities
Less Than 12 Months, Fair Value	10,511	10,699
Less Than 12 Months, Gross Unrealized Losses	281	80
12 Months or More, Fair Value	350	310
12 Months or More, Gross Unrealized Losses	150	190
Total, Fair Value	10,861	11,009
Total, Gross Unrealized Losses	$ 431	$ 270