Supplemental Cash Flow Information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Supplemental non-cash investing and financing activities:
Value of common stock issued in acquisitions	$ 1,900	$ 52,711
Value of common stock issued in payment of accrued liability	600	0
Equipment acquired through capital leases	0	691
Exercise of stock options by common stock surrender	1,005	2,418
Supplemental cash payment information:
Interest paid	710	780
Income taxes paid	$ 13,884	$ 10,157