Earnings Per Share (EPS Components) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Summary of earnings per share
Net income	$ 27,555	$ 20,725
Weighted Average Shares (in shares)
BASIC SHARES	27,486,573	27,029,640
EFFECT OF DILUTIVE SECURITIES	67,381	81,283
DILUTIVE SHARES	27,553,954	27,110,923
NET INCOME PER SHARE (in dollars per share)
BASIC EPS	$ 1.00	$ 0.77
EFFECT OF DILUTIVE SECURITIES	0.00	(0.01)
DILUTIVE EPS	$ 1.00	$ 0.76