Stock-Based Incentive Plans (Details) $ / shares in Units, $ in Thousands			6 Months Ended		12 Months Ended
	Apr. 20, 2016 $ / shares shares	Feb. 01, 2016 $ / shares shares	Jun. 30, 2016 USD ($) plan $ / shares shares	Jun. 30, 2015 USD ($)	Dec. 31, 2015 $ / shares shares
Stock-Based Compensation
Number of stock-based incentive plans | plan			1
Number of stock option plans superseded | plan			2
Aggregate Intrinsic Value
Granted (in shares)			0		0
Stock options outstanding and expected to vest			0
Total intrinsic value of options exercised (in dollars) | $			$ 700	$ 1,200
Unrecognized compensation cost and vesting period
Unrecognized compensation costs related to unvested share-based compensation arrangements | $			$ 27,100
Weighted-average period for recognition of unrecognized stock-based compensation expense			2 years 1 month 16 days
Restricted Stock Units
Stock-Based Compensation
Weighted average granted date fair value (in dollars per share) | $ / shares	$ 38.00	$ 32.63
Restricted stock unit activity
Outstanding at the beginning of the period (in shares)			527,000
Awarded (in shares)		431,439	442,000
Vested (in shares)			(340,000)
Forfeited (in shares)			(11,000)
Outstanding at the end of the period (in shares)			618,000		527,000
Outstanding and expected to vest at end of the period (in shares)			605,000
Weighted-Average Exercise Price
Weighted-average exercise price at beginning of the period (in dollars per share) | $ / shares			$ 31.56
Weighted-average exercise price at end of the period (in dollars per share) | $ / shares			31.81		$ 31.56
Outstanding and expected to vest at the end of the period (in dollars per share) | $ / shares			$ 31.81
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $			$ 24,745
Outstanding and expected to vest at end of the period (in dollars) | $			$ 24,163
Aggregate Intrinsic Value
Closing price per share (in dollars per share) | $ / shares			$ 39.97
Total intrinsic value of awards vested (in dollars) | $			$ 10,700	$ 10,100
Non-Qualified Stock Options
Non-Qualified Stock Options activity
Exercisable at the start of the period (in shares)			523,000
Exercised (in shares)			(86,000)
Forfeited (in shares)			(1,000)
Exercisable at the end of the period (in shares)			436,000		523,000
Weighted-Average Exercise Price
Weighted-average exercise price at beginning of the period (in dollars per share) | $ / shares			$ 29.55
Weighted-average exercise price at end of the period (in dollars per share) | $ / shares			$ 29.61		$ 29.55
Weighted-average remaining contractual life			1 year 6 months 19 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars) | $			$ 4,511
Aggregate Intrinsic Value
Closing price per share (in dollars per share) | $ / shares			$ 39.97
Non Employee Directors | Restricted Stock Units
Restricted stock unit activity
Awarded (in shares)	1,800