Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock options additional disclosures [Abstract]
Stock-based compensation expense	$ 3,521,000	$ 4,305,000	$ 4,364,000
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Number of shares available for future grant (in shares)	3,800,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	4 years
Stock awards termination period	10 years
Stock options [Roll Forward]
Outstanding, beginning of period (in shares)	1,341,500
Granted (in shares)	3,296
Exercised (in shares)	(290,243)
Forfeited (in shares)	(105)
Expired (in shares)	(16,106)
Outstanding, end of period (in shares)	1,038,342	1,341,500
Exercisable, end of period (in shares)	1,031,726
Expected to vest (in shares)	5,249
Stock options, weighted average exercise price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 22.98
Granted (in dollars per share)	$ 24.80
Exercised (in dollars per share)	$ 22.58
Forfeited (in dollars per share)	$ 20.19
Expired (in dollars per share)	$ 22.36
Outstanding, end of period (in dollars per share)	$ 23.10	$ 22.98
Exercisable, end of period (in dollars per share)	$ 23.09
Expected to vest (in dollars per share)	$ 24.50
Stock options additional disclosures [Abstract]
Weighted average remaining contractual term, outstanding, end of period (in years)	3 years 4 months 24 days
Weighted average remaining contractual term, exercisable, end of period (in years)	3 years 4 months 13 days
Weighted average remaining contractual term, expected to vest (in years)	7 years 3 months 25 days
Aggregate intrinsic value, outstanding, end of period	3,353,951
Aggregate intrinsic value, exercisable, end of period	3,342,258
Aggregate intrinsic value, expected to vest	9,354
Stock-based compensation expense	100,000	200,000	500,000
Proceeds from stock options exercised	6,554,000	7,927,000	1,908,000
Tax benefits related to stock options exercised	313,000	178,000	8,000
Intrinsic value of stock options exercised	789,000	905,000	498,000
Fair value of shares vested during the year	393,000	766,000	1,656,000
Restricted Stock [Member]
Stock options additional disclosures [Abstract]
Unrecognized compensation cost	4,400,000
Unrecognized compensation cost, weighted average period of recognition (in years)	1 year 8 months 12 days
Restricted stock and restricted stock units [Roll Forward]
Unvested, beginning of period (in shares)	66,650
Forfeited (in shares)	0
Vested (in shares)	(14,650)
Unvested, end of period (in shares)	52,000
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Unvested, beginning of period (in dollars per share)	$ 23.15
Forfeited (in dollars per share)	$ 0
Vested (in dollars per share)	$ 22.16
Unvested, end of period (in dollars per share)	$ 23.43
Restricted Stock [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	5 years
Restricted Stock [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years
Restricted Stock Units (RSUs) [Member]
Restricted stock and restricted stock units [Roll Forward]
Unvested, beginning of period (in shares)	539,850
Forfeited (in shares)	(5,090)
Vested (in shares)	(105,013)
Granted (in shares)	209,228
Unvested, end of period (in shares)	638,975
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Unvested, beginning of period (in dollars per share)	$ 27.36
Forfeited (in dollars per share)	$ 0
Vested (in dollars per share)	$ 0
Granted (in dollars per share)	$ 24.11
Unvested, end of period (in dollars per share)	$ 31.01
Restricted and Deferred Stock Awards [Member]
Stock options additional disclosures [Abstract]
Stock-based compensation expense	4,200,000	3,800,000	3,700,000
Tax benefit from compensation expense	$ 2,900,000	$ 2,400,000	$ 1,500,000