Stockholders' Equity (Details 2) (RSUs, USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
RSUs
Number of Shares
Balance unvested at the beginning of the period (in shares)	614,423	421,369
Granted (in shares)	21,158	263,506
Vested (in shares)		(69,994)
Forfeited (in shares)	(8,522)	(458)
Balance unvested at the end of the period (in shares)	627,059	614,423
Weighted Average Grant-Date Fair Value
Balance unvested at the beginning of the period (in dollars per share)	$ 46.22	$ 43.76
Granted (in dollars per share)	$ 52.00	$ 49.51
Vested (in dollars per share)		$ 43.76
Forfeited (in dollars per share)	$ 49.88	$ 43.76
Balance unvested at the end of the period (in dollars per share)	$ 46.46	$ 46.22