CONSOLIDATED BALANCE SHEETS CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Available-for-sale Securities, Amortized Cost Basis	$ 1,295,377	$ 1,045,337
Held-to-maturity Securities, Fair Value	$ 698,722	$ 763,575
Common Stock, No Par Value	$ 0	$ 0
Common Stock, Shares Authorized	160,000,000	160,000,000
Common Stock, Shares, Issued	68,730,731	68,730,731
Treasury Stock, Shares	6,589,660	6,751,179