Consolidated Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Held-to-maturity, fair value	$ 525,593	$ 512,705	$ 380,176
Accumulated depreciation of premises and equipment	$ 121,762	$ 120,382	$ 111,270
Preferred stock, no par value
Preferred stock, shares authorized	2,000,000	2,000,000	200,000
Preferred stock, shares issued	0	0	0
Common stock, par value	$ 1	$ 1	$ 1
Common stock, shares authorized	60,000,000	60,000,000	45,000,000
Common stock, shares issued	38,248,489	38,167,861	32,847,063
Common stock, shares outstanding	38,248,489	38,167,861	32,847,063