Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation [Abstract]
Number of common shares available for grant under the incentive plan (in shares)	997,059
Allocated Share-based Compensation Expense	$ 13,345	$ 11,053	$ 11,103
Stock option activity [Roll Forward]
Outstanding, beginning balance (in shares)	43,000
Granted (in shares)	0
Exercised (in shares)	(15,000)
Canceled (in shares)	0
Outstanding, ending balance (in shares)	28,000	43,000
Exercisable, ending balance (in shares)	28,000
Weighted average exercise price [Abstract]
Outstanding, beginning balance (in dollars per share)	$ 28.04
Granted (in dollars per share)	0.00
Exercised (in dollars per share)	25.14
Canceled (in dollars per share)	0.00
Outstanding, ending balance (in dollars per share)	29.56	$ 28.04
Exercisable, ending balance (in dollars per share)	$ 29.56
Weighted average remaining contractual life, stock option awards outstanding at end of year (in years)	4 years 5 months
Weighted average remaining contractual life, stock option awards exercisable at end of year (in years)	4 years 5 months
Aggregate intrinsic value of options outstanding, ending balance	$ 527
Aggregate intrinsic value of options exercisable ending balance	527
Intrinsic value of options exercised during the year	$ 300	$ 300	1,500
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years
Share-based compensation expense	$ 13,345	11,053	11,103
Tax benefits (expense) associated with stock-based compensation	$ 5,300	$ 4,600	$ 4,500
Employee Stock Purchase Plan (ESPP) [Abstract]
ESPP Stock Issued During Period (in shares)	24,000	37,000	34,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares vested during the year	$ 18,600	$ 10,800	$ 12,300
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 14,400
Unrecognized compensation expense, period for recognition (in months)	23 months
Equity Instruments Other than Options, Nonvested, Number of Shares[Roll Forward]
Balance at 12/31/2014 (in shares)	740,000
Granted (in shares)	271,000
Vested (in shares)	(368,000)
Canceled (in shares)	(25,000)
Balance at 12/31/2015 (in shares)	618,000	740,000
Weighted Average Grant Date Fair Value, Equity Instruments Other than Options [Abstract]
Balance at 12/31/2014 (in dollars per share)	$ 28.84
Granted (in dollars per share)	51.54	$ 28.22	$ 29.25
Vested (in dollars per share)	29.71
Canceled (in dollars per share)	36.68
Balance at 12/31/2015 (in dollars per share)	$ 37.98	$ 28.84
Restricted Stock [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years
Restricted Stock [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	5 years
Long-Term Incentive Program Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 6,000
Maximum shares eligible to receive under long-term incentive plan (LTIP) granted during the year	201,800
Maximum shares eligible to receive under LTIP as of balance sheet date	201,800
NumberofShareExpectedtoVestBasedOnCurrentEstimatesofPerformanceAchievment	153,146
Equity Instruments Other than Options, Nonvested, Number of Shares[Roll Forward]
Balance at 12/31/2014 (in shares)	0
Granted (in shares)	103,450
Vested (in shares)	0
Canceled (in shares)	(2,550)
Balance at 12/31/2015 (in shares)	100,900	0
Weighted Average Grant Date Fair Value, Equity Instruments Other than Options [Abstract]
Balance at 12/31/2014 (in dollars per share)	$ 0.00
Granted (in dollars per share)	52.80
Vested (in dollars per share)	0.00
Canceled (in dollars per share)	0.00
Balance at 12/31/2015 (in dollars per share)	$ 52.80	$ 0.00
Long-Term Incentive Program Awards [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years