Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of provision for tax from the federal rate to the effective tax rate [Abstract]
Income tax computed at statutory tax rate	$ 48,812	$ 53,008	$ 56,732
Tax exempt interest	(6,780)	(5,908)	(5,612)
Nondeductible interest expense	201	119	107
State income taxes, net	1,754	1,408	2,933
Income tax credits	(16,183)	(15,283)	(15,212)
Other	3,249	2,070	(419)
Income tax provision	$ 31,053	$ 35,414	$ 38,529