Investment Securities - Maturities of Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Securities with amortized cost pledged to secure borrowings and deposits	$ 911,900	$ 794,000
Investment Securities Available-for-Sale:
Due in one year or less, Amortized Cost	248,015
Due after one year through five years, Amortized Cost	529,893
Due after five years through ten years, Amortized Cost	347,825
Due after ten years, Amortized Cost	167,832
Preferred stock, Amortized Cost	1,389
Total Available-for-sale Securities, Debt Maturities, Amortized Cost	1,294,954
Due in one year or less , Fair Value	246,683
Due after one year through five years, Fair Value	524,707
Due after five years through ten years, Fair Value	340,248
Due after ten years, Fair Value	162,405
Preferred stock, Fair Value	1,803
Total Available-for-sale securities, Debt maturities, Fair Value	1,275,846
Investment Securities Held-to-Maturity:
Due in one year or less, Amortized Cost	70,242
Due after one year through five years, Amortized Cost	271,055
Due after five years through ten years, Amortized Cost	146,712
Due after ten years, Amortized Cost	159,183
Total Held-to-maturity securities, Debt maturities, Amortized Cost	647,192	623,427
Due in one year or less , Fair Value	70,210
Due after one year through five years, Fair Value	268,753
Due after five years through ten years, Fair Value	144,004
Due after ten years, Fair Value	156,833
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 639,800	$ 608,531