Stock option and award plan: (Tables)

12 Months Ended

Dec. 31, 2013

Stock option and award plan:

Schedule of assumptions used for determining the fair value of options granted

	Years Ended December 31,
Black-Scholes Assumptions	2013			2012			2011
Dividend yield		2.0	%		1.3	%		0.0	%
Expected volatility		58.5	%		61.6	%		63.2	%
Risk-free interest rate		0.8	%		0.7	%		1.6	%
Expected life of the option term (in years)		4.8			4.8			4.9

Schedule of stock option activity

	Number of Options			Weighted-Average Exercise Price
Outstanding at December 31, 2012		238,490		$	14.87
Granted		58,472		$	30.50
Cancelled		(32,976	)	$	21.55
Exercised—intrinsic value $1.4 million; cash received $1.2 million		(88,409	)	$	13.78
Outstanding at December 31, 2013—$3.7 million intrinsic value and 5.9 years weighted-average remaining contractual term		175,577		$	19.36
Exercisable at December 31, 2013—$2.8 million intrinsic value and 4.3 years weighted-average remaining contractual term		114,361		$	15.65
Expected to vest—$3.5 million intrinsic value and 5.6 years weighted-average remaining contractual term		160,798		$	18.42

Schedule of non-vested restricted stock awards

Non-vested awards	Shares			Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2012		1,683,588		$	16.12
Granted		175,500		$	27.82
Vested		(773,430	)	$	15.20
Forfeited		(46,335	)	$	18.06
Non-vested at December 31, 2013		1,039,323		$	18.69