Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Held-to-maturity, fair value	$ 568,415	$ 512,705	$ 466,578
Accumulated depreciation of premises and equipment	$ 121,890	$ 120,382	$ 111,270
Preferred stock, no par value
Preferred stock, shares authorized	2,000,000	2,000,000	2,000,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares authorized	60,000,000	60,000,000	60,000,000
Common stock, shares issued	38,267,118	38,167,861	38,110,136
Common stock, shares outstanding	38,267,118	38,167,861	38,110,136