Stockholders' Equity (Restricted Stock Activity) (Details) - Restricted Stock - $ / shares	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2016	Dec. 31, 2014
Shares
Outstanding, beginning of period	275,500	559,200
Shares granted	288,600	497,800
Shares vested		(171,400)
Shares forfeited	(4,900)	(58,400)
Outstanding, end of period	559,200	827,200	275,500
Weighted Average Grant Date Fair Value
Outstanding, beginning of period	$ 37.21	$ 38.09
Shares granted	39.08	33.42
Shares vested		34.65
Shares forfeited	47.16	38.56
Outstanding, end of period	$ 38.09	$ 35.96	$ 37.21
Weighted Average Remaining Vesting Period
Weighted Average Remaining Vesting Period	2 years 11 months 19 days	3 years 1 month 13 days	2 years 5 months 27 days