Share-Based Compensation: (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Non-qualified stock options
Activity in the entity's stock option plans
Granted (in shares)	0
Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	1,353
Exercised (in shares)	(155)
Forfeited and expired (in shares)	(6)
Outstanding, end of period (in shares)	1,192
Exercisable (in shares)	1,010
Weighted average exercise price
Outstanding, weighted average exercise price, beginning of period (in dollars per share)	$ 21.15
Exercised, weighted average exercise price (in dollars per share)	$ 20.48
Forfeited and expired, weighted average exercise price (in dollars per share)	$ 21.05
Outstanding, weighted average exercise price, end of period (in dollars per share)	$ 21.24
Exercisable, weighted average exercise price (in dollars per share)	$ 21.08
Outstanding, weighted average contractual life	4 years 10 months 24 days
Exercisable, weighted average contractual life	4 years 6 months
Outstanding, aggregate intrinsic value (in dollars)	$ 6,005
Exercisable, aggregate intrinsic value (in dollars)	$ 5,250
2007 Plan | Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	954
Exercised (in shares)	(106)
Forfeited and expired (in shares)	(4)
Outstanding, end of period (in shares)	844
Exercisable (in shares)	662
Predecessor Plans 1998 Plan | Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	253
Exercised (in shares)	(43)
Forfeited and expired (in shares)	(2)
Outstanding, end of period (in shares)	208
Exercisable (in shares)	208
Predecessor Plan 1998 Directors' Plan | Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	146
Exercised (in shares)	(6)
Outstanding, end of period (in shares)	140
Exercisable (in shares)	140