Equity-Based Compensation (Details 3) (Stock options, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Stock-based compensation
Contractual life	10 years
Stock options
Outstanding at the beginning of the period (in shares)	70,339
Options granted (in shares)	10,682
Outstanding at the end of the period (in shares)	81,021	70,339
Expected to vest (in shares)	81,021
Exercisable (in shares)	25,339
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 54.15
Options granted (in dollars per share)	$ 52.44
Outstanding at the end of the period (in dollars per share)	$ 53.92	$ 54.15
Expected to vest (in dollars per share)	$ 53.92
Exercisable (in dollars per share)	$ 54.15
Weighted average remaining contractual life
Outstanding at the beginning of the period	8 years 11 months 1 day	9 years 9 months 15 days
Outstanding at the end of the period	8 years 11 months 1 day	9 years 9 months 15 days
Expected to vest	8 years 11 months 1 day
Exercisable	8 years 9 months 11 days
Intrinsic Value
Outstanding at the beginning of the period	$ 653,000
Outstanding at the end of the period		653,000
Weighted-average assumptions used to calculate fair value of stock options granted
Volatility (as a percent)	40.00%	35.00%
Risk-free interest rate (as a percent)	1.75%	1.48%
Expected life	5 years 6 months	6 years 2 months 1 day
Weighted average fair value of options granted (in dollars per share)	$ 20.55	$ 20.20
Additional disclosures
Unrecognized stock-based compensation expense	$ 1,000,000
Weighted average period for recognizing unrecognized stock-based compensation expense	2 years 10 months 24 days
Minimum
Stock-based compensation
Vesting period	1 year
Maximum
Stock-based compensation
Vesting period	4 years