Employee Benefit Plans (Details 6) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended						1 Months Ended		12 Months Ended
	May 23, 2013	May 15, 2013	May 23, 2012	May 18, 2011	Apr. 20, 2011	Jan. 19, 2011	May 31, 2011	Apr. 30, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 21, 2008
Recognition and Retention Plan
Recognition and Retention Plan and Stock Option Plans
Weighted average grant date fair value of shares issued (in dollars per share)		$ 12.55	$ 11.64	$ 12.34
Market value of shares issued		$ 3.4	$ 3.1	$ 15.7
Number of shares forfeited									68,079	20,945
Vesting period							10 years		10 years
Percentage of granted awards which will vest											20.00%
Vesting period from award date									1 year
Recognition and Retention Plan | 2011 Equity Incentive Plan
Recognition and Retention Plan and Stock Option Plans
Number of shares authorized					2,806,233
Recognition and Retention Plan | 2011 issuance
Recognition and Retention Plan and Stock Option Plans
Percentage of granted awards which will vest									30.00%
Recognition and Retention Plan | 2012 issuance
Recognition and Retention Plan and Stock Option Plans
Percentage of granted awards which will vest									20.00%
Recognition and Retention Plan | 2013 issuance
Recognition and Retention Plan and Stock Option Plans
Percentage of granted awards which will vest									10.00%
Stock options
Recognition and Retention Plan and Stock Option Plans
Number of shares authorized												3,937,500
Vesting period	10 years						10 years	7 years	10 years
Vesting period from award date											1 year
Exercisable period							10 years		10 years
Number
Balance at beginning of year (in shares)									7,044,753	6,902,247	4,184,873
Granted (in shares)									590,300	573,373	3,207,191
Exercised (in shares)									(727,415)	(323,790)	(380,778)
Forfeited (in shares)									(91,344)	(107,077)	(109,039)
Balance at end of year (in shares)									6,816,294	7,044,753	6,902,247
Exercisable at end of year (in shares)									2,916,621	2,959,834	2,631,198
Weighted average exercise price
Balance at beginning of year (in dollars per share)									$ 11.21	$ 11.00	$ 9.56
Granted (in dollars per share)		$ 12.44	$ 11.70	$ 12.32	$ 12.17	$ 12.12			$ 12.44	$ 11.70	$ 12.28
Exercised (in dollars per share)									$ 10.13	$ 7.48	$ 6.06
Forfeited (in dollars per share)									$ 11.82	$ 11.31	$ 11.21
Balance at end of year (in dollars per share)									$ 11.46	$ 11.21	$ 11.00
Exercisable at end of year (in dollars per share)									$ 10.97	$ 10.61	$ 10.11
Additional disclosure
Weighted average fair value of options at grant date (in dollars per share)									$ 1.03	$ 1.23	$ 2.16
Total intrinsic value of options exercised									2.7	1.5	2.3
Aggregate intrinsic value of all options expected to vest									11.5
Aggregate intrinsic value of all options fully vested									$ 11.1
Stock options | 2011 Equity Incentive Plan
Recognition and Retention Plan and Stock Option Plans
Number of shares authorized					7,015,583
Outside Director | Recognition and Retention Plan
Recognition and Retention Plan and Stock Option Plans
Number of shares issued		29,700	24,300	108,000					29,700
Outside Director | Stock options
Number
Granted (in shares)		79,200	64,800	270,000	30,000	60,000			79,200
Employees | Recognition and Retention Plan
Recognition and Retention Plan and Stock Option Plans
Number of shares issued		240,700	239,077	1,165,949					240,700
Employees | Stock options
Number
Granted (in shares)		511,100	508,573	2,331,898		515,293			511,100