Stock-Based Compensation (Details) - $ / shares	1 Months Ended	12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016
Performance Shares [Member]
Common stock Nonvested, Number of Shares:
Unvested at beginning		33,226
Issued	36,523	36,523	34,957
Forfeited		(2,520)	(1,731)
Vested		(4,891)
Unvested at end		62,338	33,226
Common stock Nonvested, Weighted Average Grant Date Fair Value:
Unvested at beginning		$ 42.60
Issued		57.49	42.60
Forfeited		41.93	42.60
Vested		54.70
Unvested at end		$ 50.45	$ 42.60
Time Vested Awards [Member]
Common stock Nonvested, Number of Shares:
Unvested at beginning		262,966	369,093
Issued		91,097	104,775
Forfeited		(2,360)	(8,749)
Vested		(187,600)	(202,153)
Unvested at end		164,986	262,966
Common stock Nonvested, Weighted Average Grant Date Fair Value:
Unvested at beginning		$ 33.60	$ 24.43
Issued		62.70	46.39
Forfeited		49.52	39.82
Vested		30.07	23.22
Unvested at end		$ 53.57	$ 33.60