Earnings Per Share (EPS Components) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Summary of earnings per share
Net income	$ 31,118	$ 20,563	$ 58,673	$ 41,288
Weighted Average Shares (in shares)
BASIC SHARES	27,526,653	27,257,799	27,506,724	27,144,350
EFFECT OF DILUTIVE SECURITIES	54,525	74,497	61,480	78,757
DILUTIVE SHARES	27,581,178	27,332,296	27,568,204	27,223,107
NET INCOME PER SHARE (in dollars per share)
BASIC EPS	$ 1.13	$ 0.75	$ 2.13	$ 1.52
EFFECT OF DILUTIVE SECURITIES	0.00	0.00	0.00	0.00
DILUTIVE EPS	$ 1.13	$ 0.75	$ 2.13	$ 1.52