Acquisition charges

9 Months Ended

Sep. 30, 2014

Business Combination, Separately Recognized Transactions [Abstract]

Acquisition charges

Acquisition charges

We incurred various costs as a result of the 2011 acquisition of National that are included in Other for segment reporting purposes, consistent with how management measures the performance of our segments. These acquisition charges are as follows:

	For Three Months Ended September 30,				For Nine Months Ended September 30,
	2014		2013		2014		2013
Amortization of intangible assets	$	80	$	81	$	239	$	244
Stock-based compensation	3		3		9		8
Retention bonuses	—		2		—		5
Acquisition charges	$	83	$	86	$	248	$	257

Amortization of intangible assets resulting from the National acquisition is based on estimated useful lives. See Note 6 for additional information. Stock-based compensation reflects awards to former National employees and is recognized over the applicable vesting period for the remaining grantees. Retention bonuses reflect amounts paid to former National employees who fulfilled agreed-upon service period obligations and were recognized ratably over the required service period.