Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Stock-based compensation
Number of shares available for grant	3,105,328		3,016,108
Stock option / award activity
Number of shares available for grant	3,105,328		3,016,108
Stock options / awards
Stock-based compensation expense	$ 4,400	$ 3,500
Stock options
Stock-based compensation
Number of shares available for grant	3,105,328	2,559,240
Stock option / award activity
Options outstanding at the beginning of the period (in shares)	3,419,423	3,948,874	3,948,874
Granted (in shares)	0	726,000
Exercised (in shares)	(340,819)	(18,667)
Forfeited (in shares)	(39,089)	(185,197)
Options outstanding at the end of the period (in shares)	3,039,515	4,471,010	3,419,423	3,948,874
Number of shares available for grant	3,105,328	2,559,240
Total shares reserved at the end of period	6,144,843	7,030,250
Options exercisable at the end of period (in shares)	2,303,539	3,000,374
WEIGHTED-AVERAGE EXERCISE PRICE
Options outstanding at the beginning of the period (in dollars per option)	$ 26.92	$ 28.91	$ 28.91
Granted (in dollars per option)	$ 0.00	$ 18.22
Exercised (in dollars per option)	$ 24.71	$ 14.39
Forfeited (in dollars per option)	$ 22.50	$ 21.93
Options outstanding at the end of the period (in dollars per option)	$ 27.23	$ 27.52	$ 26.92	$ 28.91
Options exercisable at the end of period (in dollars per option)	$ 30.17	$ 31.97
WEIGHTED-AVERAGE REMAINING CONTRACTUAL LIFE (in years)
Weighted average remaining contractual life, Options outstanding at the end of the period	2 years 9 months 18 days	3 years	2 years 10 months 24 days	2 years 4 months 24 days
Weighted average remaining contractual life, Options exercisable at the end of the period	2 years 1 month 6 days	1 year 10 months 24 days
AGGREGATE INTRINSIC VALUE
Aggregate intrinsic value, Options outstanding at the end of the period	50,621	4,763
Aggregate intrinsic value, Options exercisable at the end of period	33,257	2,584
Stock options / awards
Stock-based compensation expense	1,100	1,100
Intrinsic values of stock options exercised	4,900	102
2011 Equity and Incentive Plan
Stock-based compensation
Number of equal annual installments in which awards vest, with performance criteria	3
2011 Equity and Incentive Plan | Maximum
Stock-based compensation
Expiration period of stock options from date of grant	7 years
Predecessor plans to the 2011 Equity and Incentive Plan | Minimum
Stock-based compensation
Expiration period of stock options from date of grant	5 years
Predecessor plans to the 2011 Equity and Incentive Plan | Maximum
Stock-based compensation
Expiration period of stock options from date of grant	10 years
2004 Non-Employee Director Stock Plan and predecessor plans | Maximum
Stock-based compensation
Expiration period of stock options from date of grant	10 years
Non-Employee Director Stock Plans
Stock options / awards
Stock-based compensation expense	210	81
2011 Non-Employee Director Stock Plan (the Director Plan)
Stock-based compensation
Number of shares authorized for issuance to each director	3,000
The maximum period of time that can elapse subsequent to a new director's appointment prior to receipt of an initial award in accordance with the plan	30 days
Number of shares available for grant	158,000		158,000
Stock option / award activity
Number of shares available for grant	158,000		158,000
Restricted stock units
Stock-based compensation
Number of equal annual installments in which awards vest, with performance criteria	3
Stock options / awards
Stock-based compensation expense	$ 3,100	$ 2,300