Stock-Based Compensation (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-Based Compensation
Stock-based compensation expense	$ 4,800,000	$ 4,000,000	$ 2,800,000
Income tax benefit	1,800,000	1,500,000	1,000,000
Shares
Balance at beginning of year (in shares)	858,000
Balance at end of year (in shares)	910,000	858,000
Weighted-Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 12.24	$ 11.59
Balance at end of year (in dollars per share)	$ 12.95	$ 12.24	$ 11.59
Stock Options
Shares
Balance at beginning of year (in shares)	858,000	1,143,000	1,056,000
Granted (in shares)	156,000	156,000	190,000
Exercised (in shares)	(104,000)	(440,000)	(103,000)
Forfeited (in shares)		(13.87)
Balance at end of year (in shares)		858,000	1,143,000
Options exercisable at end of year (in shares)	587,000	528,000	810,000
Weighted-Average Exercise Price
Balance at beginning of year (in dollars per share)	$ 12.24	$ 11.59	$ 10.84
Granted (in dollars per share)	$ 16.15	$ 13.86	$ 11.19
Exercised (in dollars per share)	$ 11.87	$ 11.10	$ 3.20
Balance at end of year (in dollars per share)		$ 12.24	$ 11.59
Other information
Intrinsic value of options exercised	400,000	3,000,000	800,000
Weighted-average remaining contractual term of options exercisable	5 years
Aggregate intrinsic value of options exercisable	2,900,000
Number of options that are vested and expected to vest (in shares)	900,000
Weighted average exercise price of options that are vested and expected to vest (in dollars per share)	$ 12.95
Weighted-average remaining contractual term of options that are vested and expected to vest	6 years 2 months 12 days
Aggregate intrinsic value of options that are vested and expected to vest	$ 3,800,000

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F