Share-Based Compensation: (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 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)	(48)
Forfeited and expired (in shares)	(8)
Outstanding, end of period (in shares)	1,297
Exercisable (in shares)	1,095
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)	$ 17.41
Forfeited and expired, weighted average exercise price (in dollars per share)	$ 21.74
Outstanding, weighted average exercise price, end of period (in dollars per share)	$ 21.28
Exercisable, weighted average exercise price (in dollars per share)	$ 21.14
Outstanding, weighted average contractual life	5 years 1 month 6 days
Exercisable, weighted average contractual life	4 years 7 months 6 days
Outstanding, aggregate intrinsic value (in dollars)	$ 4,897
Exercisable, aggregate intrinsic value (in dollars)	$ 4,307
2007 Plan | Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	954
Exercised (in shares)	(42)
Forfeited and expired (in shares)	(6)
Outstanding, end of period (in shares)	906
Exercisable (in shares)	704
Predecessor Plans 1998 Plan | Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares)	253
Forfeited and expired (in shares)	(2)
Outstanding, end of period (in shares)	251
Exercisable (in shares)	251
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