Earnings per Share/Capital Stock: (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Basic
Net income		$ 12,701	$ 10,150
Less: Distributed earnings to common shareholders		8,854	8,181
Less: Distributed earnings to participating securities		42	45
Undistributed earnings		3,805	1,924
Undistributed earnings allocated to common shareholders		3,787	1,914
Undistributed earnings allocated to participating securities		18	10
Total income available to common shareholders, basic		$ 12,641	$ 10,095
Weighted average Common Shares outstanding, basic (in shares)		36,590	36,521
Basic earnings per Common Share (in dollars per share)		$ 0.35	$ 0.28
Diluted
Total income available to common shareholders, basic		$ 12,641	$ 10,095
Undistributed earnings for dilutive stock-based awards		18	10
Total common shareholders earnings, diluted		$ 12,659	$ 10,105
Weighted average Common Shares outstanding, basic (in shares)		36,590	36,521
Stock-based compensation (in shares)	[1]	192	176
Weighted average common shares outstanding, diluted (in shares)		36,782	36,697
Diluted earnings per Common Share (in dollars per share)		$ 0.34	$ 0.28

[1] In applying the treasury stock method of reflecting the dilutive effect of outstanding stock-based compensation in the calculation of diluted EPS, 120,138 and 142,402 stock options at March 31, 2017 and 2016, respectively, were deemed to be outstanding in accordance with the accounting guidance on earnings per share. All the 194,031 and 215,129 restricted stock units at March 31, 2017 and 2016, respectively, were included in the calculation of diluted EPS for the three months ended March 31, 2017 and 2016.