Income Taxes - Reconciliation of Tax Expense at Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, at federal statutory income tax rate	35.00%	35.00%	35.00%
Income Tax Expense, Continuing Operations Income Tax Reconciliation [Abstract]
Tax expense at the statutory tax rate	$ 45,660	$ 45,365	$ 46,446
Increase (decrease) in tax resulting from:
Tax-exempt income	(4,092)	(4,255)	(3,620)
State income tax, net of federal income tax benefit	3,791	3,541	3,741
Income Tax Credits and Adjustments	(2,249)	(313)	(353)
Other, net	552	876	352
Total income tax expense	$ 43,662	$ 45,214	$ 46,566