Employee compensation (Details) (Restricted Stock Awards, USD $)	0 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Restricted Stock Awards
Restricted stock awards
Outstanding at the beginning of the period (in shares)	0	1,195,000		911,000
Exchanged (in shares)	912,000
Vested (in shares)	1,000	636,000	[1]	397,000	[2]
Granted (in shares)		1,469,000		932,000
Forfeited (in shares)		(229,000)		(251,000)
Outstanding at the end of the period (in shares)	911,000	1,799,000		1,195,000		911,000
Weighted-average grant date fair value
Outstanding at the beginning of the period (in dollars per share)	$ 0.00	$ 15.06		$ 1.14
Exchanged (in dollars per share)	$ 1.14
Vested (in dollars per share)	$ 1.11	$ 18.69	[1]	$ 1.03	[2]
Granted (in dollars per share)		$ 18.17		$ 22.90
Forfeited (in dollars per share)		$ 18.47		$ 15.61
Outstanding at the end of the period (in dollars per share)	$ 1.14	$ 19.17		$ 15.06		$ 1.14
Tax Basis		$ 0
Tax Benefit Realized from Exercise of Stock Options		0
Fair Value of awards		8,900,000
Excess Income Tax Expense		400,000		0		0
Unrecognized equity and stock-based compensation expense		$ 23,300,000
Weighted average period over which unrecognized equity and stock-based compensation expense is expected to be recognized		1 year 9 months 29 days

[1] The vesting of certain restricted stock grants could result in federal and state income tax expense or benefits related to the difference between the market price of the common stock at the date of vesting and the date of grant. The total fair value of restricted stock vested during the year ended December 31, 2013 was $8.9 million. The Company recognized excess income tax expense of $0.4 million during the year ended December 31, 2013 related to restricted stock, which was recorded as an adjustment to deferred income taxes. There were no comparative amounts recorded in the years ended December 31, 2012 or 2011

[2] Vestings in the year ended December 31, 2012 related to restricted stock awards converted in the Corporate Reorganization. Such shares have a tax basis of zero to the grantee and therefore result in no tax benefit to the Company.