Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock for restricted share awards, shares	1,159,047	1,123,720	1,203,142
Issuance of common stock for employee stock unit awards, shares	39,002	14,228
Net excess tax benefit (shortfall)	$ 2.1	$ 0.6	$ (1.5)
Awards reclassified to liability for cash settlement, shares			121,363
Issuance of common stock for the employee stock purchase plan, shares	70,924	71,587
Shares repurchased to satisfy minimum statutory withholding tax upon the net settlement of equity awards	418,135	367,367	352,051
Shares Repurchased Under Board Authorization	1,992,831	2,671,637	2,005,200