Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common stock transactions:
Stock options exercised	441,241
Common stock
Common stock transactions:
Common shares purchased and retired	1,015,389	793,077	388,101
Common shares issued	16,347	21,414	1,402,811
Non-vested common shares issued	190,239	169,577	148,278
Non-vested common shares forfeited	29,844	19,184	29,261
Stock options exercised	336,598	350,438	499,625
Shares tendered in payment of option price and income tax withholding amounts	104,643	89,358	239,665
Preferred Stock Including Additional Paid in Capital [Member]
Common stock transactions:
Stock Redeemed or Called During Period, Shares	0.00	0.00	0.00
Retained Earnings
Cash dividends declared:
Common (in dollars per share)	$ 0.88	$ 0.80	$ 0.64
Preferred (in dollars per share)	0.00%	0.00%	0.00%